IS-IS Hello and Holding Time
An IS-IS router keeps sending IIHs (IS-IS Hellos) to its neighbors at a fixed interval. The receiver brings the adjacency down if the next IIH does not arrive within the Holding Time. The hello interval and the Holding Time decide how many seconds it takes to notice a failure when hellos stop while the link itself stays up.
This article covers how the Holding Time is decided, how the standard and IOS XR defaults differ, the DIS hello, and jitter and per-level timers, then checks them on IOS XR from packet timestamps and the adjacency log.
Adjacency state transitions are covered in IS-IS Adjacency Establishment and State Transitions, DIS election in IS-IS DIS and Pseudonode, and the IIH format in IS-IS Packet Types and Header Format.
The sender decides the Holding Time
The IIH header has a Holding Time field that the sending router fills in itself. ISO/IEC 10589:2002 (2nd edition) defines the field as the “Holding Timer to be used for this Intermediate system”, and section 8.2.6 specifies what the receiver does:
The value of the holdingTimer shall be set to the holding time as reported in the Holding Time field of the Pt-Pt IIH PDU. If a neighbour is not heard from in that time, the IS shall a) purge it from the database; and b) generate an adjacencyStateChange (Down) event.
LANs work the same way (section 8.4.2.5.2), with a separate holding timer per level. In other words, how long a router waits for a neighbor is set by the IIHs the neighbor sends. Change the value on one side only, and only the time the peer waits for that side changes, so detection time differs by direction.
Standard and IOS XR defaults
The Holding Time is the hello interval times a multiplier. The standard and IOS XR combine them differently, but both end up at 30 seconds.
| Item | ISO/IEC 10589:2002 | IOS XR |
|---|---|---|
| Hello interval | iSISHelloTimer 3 s |
hello-interval 10 s |
| Multiplier | ISISHoldingMultiplier 10 (constant) |
hello-multiplier 3 |
| Holding Time | 30 s | 30 s |
| DIS hello interval | dRISISHelloTimer 1 s |
One third of hello-interval (from the IOS documentation; the IOS XR documentation does not say) |
| DIS Holding Time | 10 s | One third of the above, since the multiplier is unchanged |
The IOS XR command reference describes hello-multiplier as “Advertised hold time in IS-IS hello packets is set to the hello multiplier times the hello interval.” Both are set per interface.
RP/0/RP0/CPU0:R1(config-isis-if)#hello-interval ?
<1-65535> Hello interval in seconds, default is 10RP/0/RP0/CPU0:R1(config-isis-if)#hello-multiplier ?
<3-1000> Hello multiplier value, default is 3The DIS sends hellos three times as fast
On a LAN, the DIS builds the pseudonode LSP and sends CSNPs. If the DIS fails unnoticed, stale information about the whole LAN lingers. The standard therefore has only the DIS use a shorter timer (section 8.4.4):
For a Designated Intermediate System the value of dRISISHelloTimer is used instead of iSISHelloTimer. The Holding Time for this PDU shall therefore be set to ISISHoldingMultiplier × dRISISHelloTimer seconds. This permits failing Designated Intermediate Systems to be detected more rapidly.
Cisco’s IOS command reference states “On designated intermediate system (DIS) interfaces, only one third of the configured value is used.” The IOS XR command reference does not say this, so the DIS IIH interval and Holding Time are checked on real hardware (STEP 0). As long as the multiplier does not change, the DIS Holding Time is one third of the configured Holding Time.
Jitter and per-level timers
Periodic PDUs get jitter so that transmissions do not synchronize. Section 10.1 specifies 25% jitter and gives the example that a 10-second hello time produces “random intervals of between 7,5 and 10 s”. Whether the intervals on real hardware stay within this range is checked in STEP 0.
A router with both Level 1 and Level 2 adjacencies on a LAN sends IIHs with a separate timer per level, separately jittered (section 8.4.4). That is why hello-interval accepts level 1 to change one level only. On point-to-point links, as the IOS XR command reference puts it, “IS-IS sends only a single hello for Level 1 and Level 2”, so there is one IIH.
How long detection takes
The time from the last hello to the adjacency going down is the Holding Time minus the time since the last IIH was received. By default that is at most 30 seconds, or at most 10 seconds for the DIS. hello-interval 1 brings the Holding Time down to 3 seconds at the cost of ten times as many IIHs. Sub-second detection is done with BFD.
When the interface itself goes down, the adjacency drops immediately without waiting for the Holding Time. The Holding Time matters when the link stays up but hellos stop arriving (a switch in the path, only the peer’s process stopped, and so on).
Lab verification
Lab setup
R1 to R3 are level-1-2 (wide) in the single area 49.0001, and every link metric is 10. R1 and R2 are also connected by a point-to-point link, and all three share one LAN. R3 is the LAN DIS, pinned with priority 100. The software is XRd 26.1.1.
| Router | Lo0 | Role |
|---|---|---|
| R1 | 1.1.1.1/32 | Observer. Adjacent to R2 over point-to-point (Gi0/0/0/0) and to R2 and R3 over the LAN (Gi0/0/0/1) |
| R2 | 2.2.2.2/32 | Changes hello values and shuts interfaces |
| R3 | 3.3.3.3/32 | The LAN DIS. Connected only to the LAN |
Hellos are stopped by shutting down the interface on one side only. In this environment the peer interface stays up, so the peer keeps the adjacency until the Holding Time runs out. Detection time is measured as the gap between the last IIH in the capture and the Holdtime expired time in the peer’s syslog.
Lab STEPs
| STEP | Change | What to check |
|---|---|---|
| 0 | Defaults | IIH intervals and Holding Time: one IIH on point-to-point, per level on the LAN, and one third of the interval with 10 s for the DIS |
| 1 | Set hello-multiplier 10 on R2 point-to-point |
R2’s IIH Holding Time becomes 100, and only the time R1 waits for R2 changes |
| 2 | Shut down R2 point-to-point | R1 drops R2 100 seconds after R2’s last IIH |
| 3 | Bring R2 point-to-point back with hello-interval 1 |
IIHs arrive about every second with Holding Time 3 |
| 4 | Shut down R2 point-to-point (Holding Time 3 s) | R1 drops R2 after 3 seconds |
| 5 | Restore R2 point-to-point and shut down R2 LAN | R1 and R3 drop the non-DIS R2 per level after 30 seconds |
| 6 | Bring R2 LAN back and shut down the LAN of R3 (DIS) | R1 and R2 drop the DIS R3 after 10 seconds and elect a new DIS |
| 7 | Bring R3 LAN back and set hello-interval 5 level 1 on R1 LAN |
Only R1’s Level 1 IIHs switch to a 5-second interval |
| 8 | Revert R1 (final state) | Matches STEP 0 |
STEP 0: Defaults
Counting IIH intervals in the captures per source and PDU type gives the following.
| Link | Source | PDU | Interval (min to max) | Holding Time |
|---|---|---|---|---|
| Point-to-point | R1 / R2 | P2P HELLO | 7.53 to 9.89 s | 30 |
| LAN | R1 / R2 | L1 HELLO / L2 HELLO | 7.55 to 9.90 s | 30 |
| LAN | R3 (DIS) | L1 HELLO / L2 HELLO | 2.50 to 3.35 s | 10 |
Point-to-point IIHs are a single stream with no level distinction, while the LAN carries separate Level 1 and Level 2 IIHs. Against the default of 10 seconds the intervals are 7.53 to 9.90 seconds, inside the jitter range of the standard (7.5 to 10 s). Only the DIS R3 sends at one third of that, 2.50 to 3.35 seconds, with a Holding Time of 10 — the behavior the IOS documentation describes, and one third of the Holding Time of 30 as well. Listing the first IIHs on the LAN, only the R3 lines show a Holding Time of 10.
2 2026-09-15 12:19:25.218308Z L1 HELLO, System-ID: 0030.0300.3003 10
3 2026-09-15 12:19:25.505374Z L2 HELLO, System-ID: 0010.0100.1001 30
4 2026-09-15 12:19:26.182503Z L2 HELLO, System-ID: 0030.0300.3003 10
5 2026-09-15 12:19:27.760107Z L1 HELLO, System-ID: 0030.0300.3003 10
6 2026-09-15 12:19:28.843271Z L1 HELLO, System-ID: 0010.0100.1001 30
7 2026-09-15 12:19:29.451762Z L2 HELLO, System-ID: 0030.0300.3003 10
9 2026-09-15 12:19:30.847683Z L1 HELLO, System-ID: 0030.0300.3003 10
10 2026-09-15 12:19:31.051442Z L2 HELLO, System-ID: 0020.0200.2002 30
11 2026-09-15 12:19:31.368791Z L1 HELLO, System-ID: 0020.0200.2002 30
12 2026-09-15 12:19:32.411450Z L2 HELLO, System-ID: 0030.0300.3003 10
13 2026-09-15 12:19:33.396266Z L1 HELLO, System-ID: 0030.0300.3003 10
15 2026-09-15 12:19:35.156440Z L2 HELLO, System-ID: 0010.0100.1001 30
16 2026-09-15 12:19:35.187510Z L2 HELLO, System-ID: 0030.0300.3003 10
17 2026-09-15 12:19:36.403333Z L1 HELLO, System-ID: 0030.0300.3003 10
18 2026-09-15 12:19:36.648260Z L1 HELLO, System-ID: 0010.0100.1001 30
19 2026-09-15 12:19:37.701248Z L2 HELLO, System-ID: 0030.0300.3003 10
21 2026-09-15 12:19:39.164477Z L1 HELLO, System-ID: 0030.0300.3003 10
22 2026-09-15 12:19:39.781949Z L2 HELLO, System-ID: 0020.0200.2002 30
23 2026-09-15 12:19:40.963535Z L2 HELLO, System-ID: 0030.0300.3003 10
24 2026-09-15 12:19:41.170153Z L1 HELLO, System-ID: 0020.0200.2002 30
25 2026-09-15 12:19:42.017536Z L1 HELLO, System-ID: 0030.0300.3003 10
26 2026-09-15 12:19:43.201109Z L2 HELLO, System-ID: 0010.0100.1001 30
28 2026-09-15 12:19:43.606652Z L2 HELLO, System-ID: 0030.0300.3003 10
29 2026-09-15 12:19:44.807190Z L1 HELLO, System-ID: 0030.0300.3003 10
30 2026-09-15 12:19:46.041912Z L1 HELLO, System-ID: 0010.0100.1001 30The remaining time R1 shows for its neighbors is also at or below 10 seconds only for R3.
RP/0/RP0/CPU0:R1#show isis neighbors
Tue Sep 15 12:20:38.454 UTC
IS-IS 1 neighbors:
System Id Interface SNPA State Holdtime Type IETF-NSF
R2 Gi0/0/0/0 *PtoP* Up 22 L1L2 Capable
R2 Gi0/0/0/1 5254.009e.59f8 Up 26 L1L2 Capable
R3 Gi0/0/0/1 5254.00d9.dd85 Up 7 L1L2 Capable
Total neighbor count: 3R1’s trace records the holding timer being set each time an IIH or CSNP arrives (isis_osi_adj_process_non_iih marks a setting triggered by a non-IIH PDU). The last number is the Holding Time written in the neighbor’s IIH.
Sep 15 12:19:56.905 isis/1/hlo 0/RP0/CPU0 t4478 isis_osi_adj_process_non_iih:7023 ADJ_HOLDTIME_SET L1 Gi0/0/0/1 0030.0300.3003 10
Sep 15 12:19:57.277 isis/1/hlo 0/RP0/CPU0 t4478 isis_osi_adj_update:4775 ADJ_HOLDTIME_SET L1 Gi0/0/0/1 0030.0300.3003 10
Sep 15 12:19:57.462 isis/1/hlo 0/RP0/CPU0 t4478 isis_osi_adj_update:4775 ADJ_HOLDTIME_SET L2 Gi0/0/0/1 0030.0300.3003 10
Sep 15 12:19:59.476 isis/1/hlo 0/RP0/CPU0 t4478 isis_osi_adj_update:4775 ADJ_HOLDTIME_SET L1 Gi0/0/0/1 0020.0200.2002 30
Sep 15 12:19:59.995 isis/1/hlo 0/RP0/CPU0 t4478 isis_osi_adj_update:4775 ADJ_HOLDTIME_SET L1 Gi0/0/0/1 0030.0300.3003 10
Sep 15 12:20:00.420 isis/1/hlo 0/RP0/CPU0 t4478 isis_osi_adj_update:4775 ADJ_HOLDTIME_SET L2 Gi0/0/0/1 0030.0300.3003 10
Sep 15 12:20:01.537 isis/1/hlo 0/RP0/CPU0 t4478 isis_osi_adj_process_non_iih:7023 ADJ_HOLDTIME_SET L2 Gi0/0/0/1 0030.0300.3003 10
Sep 15 12:20:02.777 isis/1/hlo 0/RP0/CPU0 t4478 isis_osi_adj_update:4775 ADJ_HOLDTIME_SET L1 Gi0/0/0/1 0030.0300.3003 10
Sep 15 12:20:03.389 isis/1/hlo 0/RP0/CPU0 t4478 isis_osi_adj_update:4775 ADJ_HOLDTIME_SET L2 Gi0/0/0/1 0030.0300.3003 10
Sep 15 12:20:04.352 isis/1/hlo 0/RP0/CPU0 t4478 isis_osi_adj_update:4775 ADJ_HOLDTIME_SET L2 Gi0/0/0/1 0020.0200.2002 30STEP 1: Set hello-multiplier 10 on R2 point-to-point
RP/0/RP0/CPU0:R2#show configuration commit changes last 1
Tue Sep 15 12:22:39.514 UTC
!! Building configuration...
!! IOS XR Configuration 26.1.1
router isis 1
interface GigabitEthernet0/0/0/0
hello-multiplier 10
!
!
endOnly R2’s IIHs carry a Holding Time of 100, and R1’s IIHs stay at 30.
72 2026-09-15 12:24:05.470587Z P2P HELLO, System-ID: 0010.0100.1001 30
76 2026-09-15 12:24:12.349414Z P2P HELLO, System-ID: 0020.0200.2002 100
77 2026-09-15 12:24:14.144272Z P2P HELLO, System-ID: 0010.0100.1001 30
78 2026-09-15 12:24:19.926608Z P2P HELLO, System-ID: 0020.0200.2002 100
79 2026-09-15 12:24:23.925439Z P2P HELLO, System-ID: 0010.0100.1001 30
80 2026-09-15 12:24:27.585106Z P2P HELLO, System-ID: 0020.0200.2002 100
81 2026-09-15 12:24:31.604166Z P2P HELLO, System-ID: 0010.0100.1001 30
82 2026-09-15 12:24:36.722906Z P2P HELLO, System-ID: 0020.0200.2002 100
83 2026-09-15 12:24:40.854072Z P2P HELLO, System-ID: 0010.0100.1001 30
84 2026-09-15 12:24:46.522196Z P2P HELLO, System-ID: 0020.0200.2002 100
85 2026-09-15 12:24:48.605837Z P2P HELLO, System-ID: 0010.0100.1001 30
86 2026-09-15 12:24:54.607219Z P2P HELLO, System-ID: 0020.0200.2002 100
87 2026-09-15 12:24:57.348143Z P2P HELLO, System-ID: 0010.0100.1001 30
88 2026-09-15 12:25:03.813903Z P2P HELLO, System-ID: 0020.0200.2002 100
89 2026-09-15 12:25:05.616892Z P2P HELLO, System-ID: 0010.0100.1001 30R1 waits 100 seconds for R2, while R2 waits 30 seconds for R1. Only R2 was configured.
RP/0/RP0/CPU0:R1#show isis neighbors
Tue Sep 15 12:23:45.420 UTC
IS-IS 1 neighbors:
System Id Interface SNPA State Holdtime Type IETF-NSF
R2 Gi0/0/0/0 *PtoP* Up 99 L1L2 Capable
R2 Gi0/0/0/1 5254.009e.59f8 Up 22 L1L2 Capable
R3 Gi0/0/0/1 5254.00d9.dd85 Up 8 L1L2 Capable
Total neighbor count: 3RP/0/RP0/CPU0:R2#show isis neighbors
Tue Sep 15 12:24:24.517 UTC
IS-IS 1 neighbors:
System Id Interface SNPA State Holdtime Type IETF-NSF
R1 Gi0/0/0/0 *PtoP* Up 29 L1L2 Capable
R1 Gi0/0/0/1 5254.00d6.fa13 Up 23 L1L2 Capable
R3 Gi0/0/0/1 5254.00d9.dd85 Up 8 L1L2 Capable
Total neighbor count: 3STEP 2: Shut down R2 point-to-point
RP/0/RP0/CPU0:R2#show configuration commit changes last 1
Tue Sep 15 12:25:52.259 UTC
!! Building configuration...
!! IOS XR Configuration 26.1.1
interface GigabitEthernet0/0/0/0
shutdown
!
endThe last IIH from R2 in the capture is at 12:25:47.261 (Holding Time 100).
1 2026-09-15 12:25:47.261127Z P2P HELLO, System-ID: 0020.0200.2002 100
2 2026-09-15 12:25:47.595139Z P2P HELLO, System-ID: 0010.0100.1001 30
3 2026-09-15 12:25:55.965890Z P2P HELLO, System-ID: 0010.0100.1001 30
4 2026-09-15 12:26:05.882241Z P2P HELLO, System-ID: 0010.0100.1001 30
5 2026-09-15 12:26:13.652706Z P2P HELLO, System-ID: 0010.0100.1001 30
6 2026-09-15 12:26:21.404311Z P2P HELLO, System-ID: 0010.0100.1001 30
7 2026-09-15 12:26:29.086369Z P2P HELLO, System-ID: 0010.0100.1001 30
8 2026-09-15 12:26:36.659607Z P2P HELLO, System-ID: 0010.0100.1001 30
10 2026-09-15 12:26:46.177144Z P2P HELLO, System-ID: 0010.0100.1001 30
11 2026-09-15 12:26:55.604216Z P2P HELLO, System-ID: 0010.0100.1001 30
12 2026-09-15 12:27:05.481751Z P2P HELLO, System-ID: 0010.0100.1001 30
13 2026-09-15 12:27:14.588652Z P2P HELLO, System-ID: 0010.0100.1001 30
14 2026-09-15 12:27:23.183526Z P2P HELLO, System-ID: 0010.0100.1001 30
15 2026-09-15 12:27:27.565213Z P2P HELLO, System-ID: 0010.0100.1001 30
16 2026-09-15 12:27:35.985846Z P2P HELLO, System-ID: 0010.0100.1001 30
18 2026-09-15 12:27:45.665727Z P2P HELLO, System-ID: 0010.0100.1001 30
19 2026-09-15 12:27:55.149472Z P2P HELLO, System-ID: 0010.0100.1001 30
20 2026-09-15 12:28:04.534515Z P2P HELLO, System-ID: 0010.0100.1001 30
21 2026-09-15 12:28:12.897484Z P2P HELLO, System-ID: 0010.0100.1001 30
23 2026-09-15 12:28:22.510994Z P2P HELLO, System-ID: 0010.0100.1001 30
24 2026-09-15 12:28:30.929919Z P2P HELLO, System-ID: 0010.0100.1001 30
25 2026-09-15 12:28:39.497327Z P2P HELLO, System-ID: 0010.0100.1001 30
26 2026-09-15 12:28:47.593149Z P2P HELLO, System-ID: 0010.0100.1001 30
27 2026-09-15 12:28:57.088905Z P2P HELLO, System-ID: 0010.0100.1001 30
28 2026-09-15 12:29:05.252406Z P2P HELLO, System-ID: 0010.0100.1001 30
29 2026-09-15 12:29:13.254265Z P2P HELLO, System-ID: 0010.0100.1001 30
30 2026-09-15 12:29:23.013393Z P2P HELLO, System-ID: 0010.0100.1001 30R1 dropped R2 at 12:27:27.263, 100.0 seconds after the last IIH. There is only one point-to-point adjacency, so Level 2 went down at the same moment (shown with the reason Interface state down). R2, which shut its own interface, dropped the adjacency immediately.
RP/0/RP0/CPU0:R1#show logging start Sep 15 12:24:19
Tue Sep 15 12:28:13.407 UTC
Time Zone UTC, DST disabled
Syslog logging: enabled (0 messages dropped, 0 flushes, 0 overruns)
Console logging: Disabled
Monitor logging: level debugging, 0 messages logged
Trap logging: level informational, 0 messages logged
Buffer logging: level debugging, 130 messages logged
Log Buffer (2097152 bytes):
RP/0/RP0/CPU0:Sep 15 12:24:19.516 UTC: logger[68504]: %OS-SYSLOG-6-LOG_INFO : informational STEP2-BEGIN
RP/0/RP0/CPU0:Sep 15 12:24:19.996 UTC: ssh_syslog_proxy[1188]: %SECURITY-SSHD_SYSLOG_PRX-6-INFO_GENERAL : sshd[6989]: Received disconnect from 10.100.3.1 port 51774:11: disconnected by user
RP/0/RP0/CPU0:Sep 15 12:24:19.996 UTC: ssh_syslog_proxy[1188]: %SECURITY-SSHD_SYSLOG_PRX-6-INFO_GENERAL : sshd[6989]: Disconnected from user cisco 10.100.3.1 port 51774
RP/0/RP0/CPU0:Sep 15 12:27:27.263 UTC: isis[1003]: %ROUTING-ISIS-5-ADJCHANGE : ISIS (1): Adjacency to R2 (GigabitEthernet0/0/0/0) (L1) Down, Holdtime expired
RP/0/RP0/CPU0:Sep 15 12:27:27.263 UTC: isis[1003]: %ROUTING-ISIS-5-ADJCHANGE : ISIS (1): Adjacency to R2 (GigabitEthernet0/0/0/0) (L2) Down, Interface state down
RP/0/RP0/CPU0:Sep 15 12:28:04.526 UTC: ssh_syslog_proxy[1188]: %SECURITY-SSHD_SYSLOG_PRX-6-INFO_GENERAL : sshd[7338]: Accepted authentication/pam for cisco from 10.100.3.1 port 51890 ssh2
RP/0/RP0/CPU0:Sep 15 12:28:10.322 UTC: ssh_syslog_proxy[1188]: %SECURITY-SSHD_SYSLOG_PRX-6-INFO_GENERAL : sshd[7343]: Received disconnect from 10.100.3.1 port 51890:11: disconnected by user
RP/0/RP0/CPU0:Sep 15 12:28:10.322 UTC: ssh_syslog_proxy[1188]: %SECURITY-SSHD_SYSLOG_PRX-6-INFO_GENERAL : sshd[7343]: Disconnected from user cisco 10.100.3.1 port 51890
RP/0/RP0/CPU0:Sep 15 12:28:11.145 UTC: ssh_syslog_proxy[1188]: %SECURITY-SSHD_SYSLOG_PRX-6-INFO_GENERAL : sshd[7449]: Accepted authentication/pam for cisco from 10.100.3.1 port 51894 ssh2 STEP 3: Bring R2 point-to-point back with hello-interval 1
RP/0/RP0/CPU0:R2#show configuration commit changes last 1
Tue Sep 15 12:30:16.959 UTC
!! Building configuration...
!! IOS XR Configuration 26.1.1
interface GigabitEthernet0/0/0/0
no shutdown
!
router isis 1
interface GigabitEthernet0/0/0/0
hello-interval 1
no hello-multiplier 10
!
!
endR2’s IIHs now carry a Holding Time of 3 (1 s × 3) and arrive about every second. Excluding the moments right after the adjacency came up, the 151 intervals in this test ranged from 0.751 to 1.249 seconds, spread on both sides of 1 second rather than the 7.53 to 9.90 seconds seen with the 10-second interval.
116 2026-09-15 12:31:40.083787Z P2P HELLO, System-ID: 0020.0200.2002 3
117 2026-09-15 12:31:40.955124Z P2P HELLO, System-ID: 0020.0200.2002 3
168 2026-09-15 12:31:42.084319Z P2P HELLO, System-ID: 0020.0200.2002 3
169 2026-09-15 12:31:42.858952Z P2P HELLO, System-ID: 0020.0200.2002 3
172 2026-09-15 12:31:44.084515Z P2P HELLO, System-ID: 0020.0200.2002 3
173 2026-09-15 12:31:45.059146Z P2P HELLO, System-ID: 0020.0200.2002 3
175 2026-09-15 12:31:46.084721Z P2P HELLO, System-ID: 0020.0200.2002 3
176 2026-09-15 12:31:47.071470Z P2P HELLO, System-ID: 0020.0200.2002 3
178 2026-09-15 12:31:48.085270Z P2P HELLO, System-ID: 0020.0200.2002 3
179 2026-09-15 12:31:48.914792Z P2P HELLO, System-ID: 0020.0200.2002 3
180 2026-09-15 12:31:50.086052Z P2P HELLO, System-ID: 0020.0200.2002 3
181 2026-09-15 12:31:50.944246Z P2P HELLO, System-ID: 0020.0200.2002 3STEP 4: Shut down R2 point-to-point (Holding Time 3 s)
R2’s last IIH is at 12:33:38.970.
1 2026-09-15 12:33:34.101702Z P2P HELLO, System-ID: 0020.0200.2002 3
2 2026-09-15 12:33:34.960218Z P2P HELLO, System-ID: 0020.0200.2002 3
3 2026-09-15 12:33:36.102182Z P2P HELLO, System-ID: 0020.0200.2002 3
4 2026-09-15 12:33:36.861245Z P2P HELLO, System-ID: 0020.0200.2002 3
5 2026-09-15 12:33:37.469747Z P2P HELLO, System-ID: 0010.0100.1001 30
6 2026-09-15 12:33:38.102034Z P2P HELLO, System-ID: 0020.0200.2002 3
7 2026-09-15 12:33:38.970468Z P2P HELLO, System-ID: 0020.0200.2002 3
8 2026-09-15 12:33:42.273982Z P2P HELLO, System-ID: 0010.0100.1001 30
9 2026-09-15 12:33:51.176488Z P2P HELLO, System-ID: 0010.0100.1001 30
10 2026-09-15 12:34:00.177671Z P2P HELLO, System-ID: 0010.0100.1001 30
11 2026-09-15 12:34:09.132580Z P2P HELLO, System-ID: 0010.0100.1001 30
12 2026-09-15 12:34:18.560256Z P2P HELLO, System-ID: 0010.0100.1001 30
13 2026-09-15 12:34:27.121507Z P2P HELLO, System-ID: 0010.0100.1001 30
14 2026-09-15 12:34:35.621316Z P2P HELLO, System-ID: 0010.0100.1001 30
15 2026-09-15 12:34:43.220786Z P2P HELLO, System-ID: 0010.0100.1001 30
16 2026-09-15 12:34:52.954360Z P2P HELLO, System-ID: 0010.0100.1001 30
17 2026-09-15 12:35:00.929311Z P2P HELLO, System-ID: 0010.0100.1001 30
18 2026-09-15 12:35:09.284229Z P2P HELLO, System-ID: 0010.0100.1001 30
19 2026-09-15 12:35:18.041913Z P2P HELLO, System-ID: 0010.0100.1001 30
20 2026-09-15 12:35:26.031302Z P2P HELLO, System-ID: 0010.0100.1001 30R1 dropped R2 at 12:33:41.972, 3.0 seconds later.
RP/0/RP0/CPU0:R1#show logging start Sep 15 12:31:53
Tue Sep 15 12:34:16.451 UTC
Time Zone UTC, DST disabled
Syslog logging: enabled (0 messages dropped, 0 flushes, 0 overruns)
Console logging: Disabled
Monitor logging: level debugging, 0 messages logged
Trap logging: level informational, 0 messages logged
Buffer logging: level debugging, 172 messages logged
Log Buffer (2097152 bytes):
RP/0/RP0/CPU0:Sep 15 12:31:53.816 UTC: logger[65894]: %OS-SYSLOG-6-LOG_INFO : informational STEP4-BEGIN
RP/0/RP0/CPU0:Sep 15 12:31:54.234 UTC: ssh_syslog_proxy[1188]: %SECURITY-SSHD_SYSLOG_PRX-6-INFO_GENERAL : sshd[8503]: Received disconnect from 10.100.3.1 port 52024:11: disconnected by user
RP/0/RP0/CPU0:Sep 15 12:31:54.235 UTC: ssh_syslog_proxy[1188]: %SECURITY-SSHD_SYSLOG_PRX-6-INFO_GENERAL : sshd[8503]: Disconnected from user cisco 10.100.3.1 port 52024
RP/0/RP0/CPU0:Sep 15 12:33:41.972 UTC: isis[1003]: %ROUTING-ISIS-5-ADJCHANGE : ISIS (1): Adjacency to R2 (GigabitEthernet0/0/0/0) (L1) Down, Holdtime expired
RP/0/RP0/CPU0:Sep 15 12:33:41.972 UTC: isis[1003]: %ROUTING-ISIS-5-ADJCHANGE : ISIS (1): Adjacency to R2 (GigabitEthernet0/0/0/0) (L2) Down, Interface state down
RP/0/RP0/CPU0:Sep 15 12:34:07.320 UTC: ssh_syslog_proxy[1188]: %SECURITY-SSHD_SYSLOG_PRX-6-INFO_GENERAL : sshd[8753]: Accepted authentication/pam for cisco from 10.100.3.1 port 52112 ssh2
RP/0/RP0/CPU0:Sep 15 12:34:13.221 UTC: ssh_syslog_proxy[1188]: %SECURITY-SSHD_SYSLOG_PRX-6-INFO_GENERAL : sshd[8758]: Received disconnect from 10.100.3.1 port 52112:11: disconnected by user
RP/0/RP0/CPU0:Sep 15 12:34:13.221 UTC: ssh_syslog_proxy[1188]: %SECURITY-SSHD_SYSLOG_PRX-6-INFO_GENERAL : sshd[8758]: Disconnected from user cisco 10.100.3.1 port 52112
RP/0/RP0/CPU0:Sep 15 12:34:14.243 UTC: ssh_syslog_proxy[1188]: %SECURITY-SSHD_SYSLOG_PRX-6-INFO_GENERAL : sshd[8864]: Accepted authentication/pam for cisco from 10.100.3.1 port 52118 ssh2 STEP 5: Restore R2 point-to-point and shut down R2 LAN
RP/0/RP0/CPU0:R2#show configuration commit changes last 1
Tue Sep 15 12:36:08.699 UTC
!! Building configuration...
!! IOS XR Configuration 26.1.1
interface GigabitEthernet0/0/0/0
no shutdown
!
interface GigabitEthernet0/0/0/1
shutdown
!
router isis 1
interface GigabitEthernet0/0/0/0
no hello-interval 1
!
!
endR2’s last IIHs are at 12:36:06.184 for Level 1 and 12:36:06.259 for Level 2.
6 2026-09-15 12:36:06.183826Z L1 HELLO, System-ID: 0020.0200.2002 30
7 2026-09-15 12:36:06.258975Z L2 HELLO, System-ID: 0020.0200.2002 30R1 (and R3 at the same times) dropped Level 1 at 12:36:36.185 and Level 2 at 12:36:36.260, each 30.0 seconds after the last IIH of that level.
RP/0/RP0/CPU0:R1#show logging start Sep 15 12:34:44
Tue Sep 15 12:37:20.305 UTC
Time Zone UTC, DST disabled
Syslog logging: enabled (0 messages dropped, 0 flushes, 0 overruns)
Console logging: Disabled
Monitor logging: level debugging, 0 messages logged
Trap logging: level informational, 0 messages logged
Buffer logging: level debugging, 195 messages logged
Log Buffer (2097152 bytes):
RP/0/RP0/CPU0:Sep 15 12:34:44.601 UTC: logger[66613]: %OS-SYSLOG-6-LOG_INFO : informational STEP5-BEGIN
RP/0/RP0/CPU0:Sep 15 12:34:44.906 UTC: ssh_syslog_proxy[1188]: %SECURITY-SSHD_SYSLOG_PRX-6-INFO_GENERAL : sshd[9223]: Received disconnect from 10.100.3.1 port 52137:11: disconnected by user
RP/0/RP0/CPU0:Sep 15 12:34:44.907 UTC: ssh_syslog_proxy[1188]: %SECURITY-SSHD_SYSLOG_PRX-6-INFO_GENERAL : sshd[9223]: Disconnected from user cisco 10.100.3.1 port 52137
RP/0/RP0/CPU0:Sep 15 12:36:08.677 UTC: isis[1003]: %ROUTING-ISIS-5-ADJCHANGE : ISIS (1): Adjacency to R2 (GigabitEthernet0/0/0/0) (L1) Up, New adjacency
RP/0/RP0/CPU0:Sep 15 12:36:08.677 UTC: isis[1003]: %ROUTING-ISIS-5-ADJCHANGE : ISIS (1): Adjacency to R2 (GigabitEthernet0/0/0/0) (L2) Up, New adjacency
RP/0/RP0/CPU0:Sep 15 12:36:36.185 UTC: isis[1003]: %ROUTING-ISIS-5-ADJCHANGE : ISIS (1): Adjacency to R2 (GigabitEthernet0/0/0/1) (L1) Down, Holdtime expired
RP/0/RP0/CPU0:Sep 15 12:36:36.260 UTC: isis[1003]: %ROUTING-ISIS-5-ADJCHANGE : ISIS (1): Adjacency to R2 (GigabitEthernet0/0/0/1) (L2) Down, Holdtime expired
RP/0/RP0/CPU0:Sep 15 12:37:11.116 UTC: ssh_syslog_proxy[1188]: %SECURITY-SSHD_SYSLOG_PRX-6-INFO_GENERAL : sshd[9435]: Accepted authentication/pam for cisco from 10.100.3.1 port 52246 ssh2
RP/0/RP0/CPU0:Sep 15 12:37:17.301 UTC: ssh_syslog_proxy[1188]: %SECURITY-SSHD_SYSLOG_PRX-6-INFO_GENERAL : sshd[9440]: Received disconnect from 10.100.3.1 port 52246:11: disconnected by user
RP/0/RP0/CPU0:Sep 15 12:37:17.301 UTC: ssh_syslog_proxy[1188]: %SECURITY-SSHD_SYSLOG_PRX-6-INFO_GENERAL : sshd[9440]: Disconnected from user cisco 10.100.3.1 port 52246
RP/0/RP0/CPU0:Sep 15 12:37:18.353 UTC: ssh_syslog_proxy[1188]: %SECURITY-SSHD_SYSLOG_PRX-6-INFO_GENERAL : sshd[9558]: Accepted authentication/pam for cisco from 10.100.3.1 port 52251 ssh2 STEP 6: Bring R2 LAN back and shut down the LAN of R3 (DIS)
R3’s last IIHs are at 12:40:33.896 for Level 1 and 12:40:34.096 for Level 2, followed by a Level 2 CSNP at 12:40:34.214.
108 2026-09-15 12:40:25.009549Z L2 CSNP, Source-ID: 0030.0300.3003.00, Start LSP-ID: 0000.0000.0000.00-00, End LSP-ID: ffff.ffff.ffff.ff-ff
110 2026-09-15 12:40:25.704463Z L2 HELLO, System-ID: 0030.0300.3003 10
111 2026-09-15 12:40:27.480395Z L1 HELLO, System-ID: 0030.0300.3003 10
112 2026-09-15 12:40:27.649419Z L1 CSNP, Source-ID: 0030.0300.3003.00, Start LSP-ID: 0000.0000.0000.00-00, End LSP-ID: ffff.ffff.ffff.ff-ff
113 2026-09-15 12:40:28.237130Z L2 HELLO, System-ID: 0030.0300.3003 10
114 2026-09-15 12:40:30.700931Z L1 HELLO, System-ID: 0030.0300.3003 10
117 2026-09-15 12:40:31.499778Z L2 HELLO, System-ID: 0030.0300.3003 10
119 2026-09-15 12:40:33.896238Z L1 HELLO, System-ID: 0030.0300.3003 10
120 2026-09-15 12:40:34.096263Z L2 HELLO, System-ID: 0030.0300.3003 10
121 2026-09-15 12:40:34.213581Z L2 CSNP, Source-ID: 0030.0300.3003.00, Start LSP-ID: 0000.0000.0000.00-00, End LSP-ID: ffff.ffff.ffff.ff-ff R1 (and R2 at the same times) dropped Level 1 at 12:40:43.898 and Level 2 at 12:40:44.215. Level 1 went down 10.0 seconds after the last IIH, and Level 2 10.0 seconds after the last CSNP received.
RP/0/RP0/CPU0:R1#show logging start Sep 15 12:37:48
Tue Sep 15 12:41:26.942 UTC
Time Zone UTC, DST disabled
Syslog logging: enabled (0 messages dropped, 0 flushes, 0 overruns)
Console logging: Disabled
Monitor logging: level debugging, 0 messages logged
Trap logging: level informational, 0 messages logged
Buffer logging: level debugging, 218 messages logged
Log Buffer (2097152 bytes):
RP/0/RP0/CPU0:Sep 15 12:37:48.604 UTC: logger[67302]: %OS-SYSLOG-6-LOG_INFO : informational STEP6-BEGIN
RP/0/RP0/CPU0:Sep 15 12:37:49.008 UTC: ssh_syslog_proxy[1188]: %SECURITY-SSHD_SYSLOG_PRX-6-INFO_GENERAL : sshd[9911]: Received disconnect from 10.100.3.1 port 52266:11: disconnected by user
RP/0/RP0/CPU0:Sep 15 12:37:49.008 UTC: ssh_syslog_proxy[1188]: %SECURITY-SSHD_SYSLOG_PRX-6-INFO_GENERAL : sshd[9911]: Disconnected from user cisco 10.100.3.1 port 52266
RP/0/RP0/CPU0:Sep 15 12:39:29.593 UTC: isis[1003]: %ROUTING-ISIS-5-ADJCHANGE : ISIS (1): Adjacency to R2 (GigabitEthernet0/0/0/1) (L1) Up, New adjacency
RP/0/RP0/CPU0:Sep 15 12:39:29.593 UTC: isis[1003]: %ROUTING-ISIS-5-ADJCHANGE : ISIS (1): Adjacency to R2 (GigabitEthernet0/0/0/1) (L2) Up, New adjacency
RP/0/RP0/CPU0:Sep 15 12:40:43.898 UTC: isis[1003]: %ROUTING-ISIS-5-ADJCHANGE : ISIS (1): Adjacency to R3 (GigabitEthernet0/0/0/1) (L1) Down, Holdtime expired
RP/0/RP0/CPU0:Sep 15 12:40:44.215 UTC: isis[1003]: %ROUTING-ISIS-5-ADJCHANGE : ISIS (1): Adjacency to R3 (GigabitEthernet0/0/0/1) (L2) Down, Holdtime expired
RP/0/RP0/CPU0:Sep 15 12:41:18.102 UTC: ssh_syslog_proxy[1188]: %SECURITY-SSHD_SYSLOG_PRX-6-INFO_GENERAL : sshd[10227]: Accepted authentication/pam for cisco from 10.100.3.1 port 52388 ssh2
RP/0/RP0/CPU0:Sep 15 12:41:24.009 UTC: ssh_syslog_proxy[1188]: %SECURITY-SSHD_SYSLOG_PRX-6-INFO_GENERAL : sshd[10232]: Received disconnect from 10.100.3.1 port 52388:11: disconnected by user
RP/0/RP0/CPU0:Sep 15 12:41:24.009 UTC: ssh_syslog_proxy[1188]: %SECURITY-SSHD_SYSLOG_PRX-6-INFO_GENERAL : sshd[10232]: Disconnected from user cisco 10.100.3.1 port 52388
RP/0/RP0/CPU0:Sep 15 12:41:25.021 UTC: ssh_syslog_proxy[1188]: %SECURITY-SSHD_SYSLOG_PRX-6-INFO_GENERAL : sshd[10349]: Accepted authentication/pam for cisco from 10.100.3.1 port 52408 ssh2 In R1’s trace, the holding timer is set to 10 again at 12:40:34.215, when the CSNP arrived. The standard specifies setting the holding timer on receipt of an IIH, but this router also reset it on a CSNP from the same neighbor.
Sep 15 12:40:31.501 isis/1/hlo 0/RP0/CPU0 t4478 isis_osi_adj_update:4775 ADJ_HOLDTIME_SET L2 Gi0/0/0/1 0030.0300.3003 10
Sep 15 12:40:31.659 isis/1/hlo 0/RP0/CPU0 t4478 isis_osi_adj_update:4775 ADJ_HOLDTIME_SET L1 Gi0/0/0/1 0020.0200.2002 30
Sep 15 12:40:33.570 isis/1/hlo 0/RP0/CPU0 t4478 isis_osi_adj_update:4775 ADJ_HOLDTIME_SET L1 Gi0/0/0/0 0020.0200.2002 30
Sep 15 12:40:33.570 isis/1/hlo 0/RP0/CPU0 t4478 isis_osi_adj_update:4775 ADJ_HOLDTIME_SET L2 Gi0/0/0/0 0020.0200.2002 30
Sep 15 12:40:33.898 isis/1/hlo 0/RP0/CPU0 t4478 isis_osi_adj_update:4775 ADJ_HOLDTIME_SET L1 Gi0/0/0/1 0030.0300.3003 10
Sep 15 12:40:34.098 isis/1/hlo 0/RP0/CPU0 t4478 isis_osi_adj_update:4775 ADJ_HOLDTIME_SET L2 Gi0/0/0/1 0030.0300.3003 10
Sep 15 12:40:34.215 isis/1/hlo 0/RP0/CPU0 t4478 isis_osi_adj_process_non_iih:7023 ADJ_HOLDTIME_SET L2 Gi0/0/0/1 0030.0300.3003 10The DIS moved to R1, which has the higher SNPA of R1 and R2 at the same priority 64. From here R1’s IIHs carry a Holding Time of 10 at 2.50 to 3.31 second intervals.
LAN ID: R1.01
Priority (Local/DIS): 64/64STEP 7: Bring R3 LAN back and set hello-interval 5 level 1 on R1 LAN
RP/0/RP0/CPU0:R1#show configuration commit changes last 1
Tue Sep 15 12:45:34.374 UTC
!! Building configuration...
!! IOS XR Configuration 26.1.1
router isis 1
interface GigabitEthernet0/0/0/1
hello-interval 5 level 1
!
!
endAfter R3 took back the DIS role, R1’s Level 1 IIHs carry a Holding Time of 15 (5 × 3) at 3.72 to 4.99 second intervals, while its Level 2 IIHs stay at 30 and 7.53 to 9.84 seconds.
172 2026-09-15 12:46:03.616174Z L1 HELLO, System-ID: 0010.0100.1001 15
176 2026-09-15 12:46:05.687481Z L2 HELLO, System-ID: 0010.0100.1001 30
180 2026-09-15 12:46:08.406971Z L1 HELLO, System-ID: 0010.0100.1001 15
185 2026-09-15 12:46:12.185327Z L1 HELLO, System-ID: 0010.0100.1001 15
187 2026-09-15 12:46:14.168501Z L2 HELLO, System-ID: 0010.0100.1001 30
192 2026-09-15 12:46:16.545735Z L1 HELLO, System-ID: 0010.0100.1001 15
198 2026-09-15 12:46:20.518774Z L1 HELLO, System-ID: 0010.0100.1001 15
200 2026-09-15 12:46:22.346369Z L2 HELLO, System-ID: 0010.0100.1001 30
205 2026-09-15 12:46:25.122224Z L1 HELLO, System-ID: 0010.0100.1001 15
211 2026-09-15 12:46:29.502120Z L1 HELLO, System-ID: 0010.0100.1001 15 Level-1
Adjacency Count: 1
Adjacency Flaps: 2
LSP Pacing Interval: 33 ms
PSNP Entry Queue Size: 0
Hello Interval: 10 s
Hello Multiplier: 3
Level-2
Adjacency Count: 1
Adjacency Flaps: 2
LSP Pacing Interval: 33 ms
PSNP Entry Queue Size: 0
Hello Interval: 10 s
Hello Multiplier: 3
CLNS I/O
Protocol State: UpSTEP 8: Revert R1 (final state)
RP/0/RP0/CPU0:R1#show configuration commit changes last 1
Tue Sep 15 12:49:21.553 UTC
!! Building configuration...
!! IOS XR Configuration 26.1.1
router isis 1
interface GigabitEthernet0/0/0/1
no hello-interval 5 level 1
!
!
endThe final configuration of all three routers matches STEP 0.
Verification configs and show output
Each STEP was captured from all three routers as separate files per router. The verification config is the ..._run.txt (the final state is the one from the last STEP).
| File | Contents |
|---|---|
..._show.txt |
show version, show interface description, show route, show route isis, the show isis set (interface, neighbors, neighbors detail, database, database detail, statistics, adjacency-log), show running-config router isis and show configuration commit list |
..._log.txt |
show logging narrowed to that STEP. A logmsg marker is placed at the start of each STEP and its timestamp passed to show logging start. R2 commit times (%MGBL-CONFIG-6-DB_COMMIT) are here too |
..._run.txt |
show running-config at that STEP (the verification config for that STEP) |
..._trace.txt |
show isis trace all | include ADJ_HOLDTIME_SET | utility tail -n 80 (the Holding Time of each received IIH) and include ADJ_CHANGE_STATE |
..._ping.txt |
From R1: ping 2.2.2.2, ping 3.3.3.3 and traceroute (source 1.1.1.1). None for R2 and R3 |
..._commit.cfg |
What was committed in that STEP (show configuration commit changes last 1). Absent for routers that changed nothing |
STEP 0: Defaults
| Router | show | syslog | running-config | trace | ping | commit |
|---|---|---|---|---|---|---|
| R1 | show | log | run | trace | ping | - |
| R2 | show | log | run | trace | - | - |
| R3 | show | log | run | trace | - | - |
STEP 1: Set hello-multiplier 10 on R2 point-to-point
| Router | show | syslog | running-config | trace | ping | commit |
|---|---|---|---|---|---|---|
| R1 | show | log | run | trace | ping | - |
| R2 | show | log | run | trace | - | commit |
| R3 | show | log | run | trace | - | - |
STEP 2: Shut down R2 point-to-point
| Router | show | syslog | running-config | trace | ping | commit |
|---|---|---|---|---|---|---|
| R1 | show | log | run | trace | ping | - |
| R2 | show | log | run | trace | - | commit |
| R3 | show | log | run | trace | - | - |
STEP 3: Bring R2 point-to-point back with hello-interval 1
| Router | show | syslog | running-config | trace | ping | commit |
|---|---|---|---|---|---|---|
| R1 | show | log | run | trace | ping | - |
| R2 | show | log | run | trace | - | commit |
| R3 | show | log | run | trace | - | - |
STEP 4: Shut down R2 point-to-point (Holding Time 3 s)
| Router | show | syslog | running-config | trace | ping | commit |
|---|---|---|---|---|---|---|
| R1 | show | log | run | trace | ping | - |
| R2 | show | log | run | trace | - | commit |
| R3 | show | log | run | trace | - | - |
STEP 5: Restore R2 point-to-point and shut down R2 LAN
| Router | show | syslog | running-config | trace | ping | commit |
|---|---|---|---|---|---|---|
| R1 | show | log | run | trace | ping | - |
| R2 | show | log | run | trace | - | commit |
| R3 | show | log | run | trace | - | - |
STEP 6: Bring R2 LAN back and shut down the LAN of R3 (DIS)
| Router | show | syslog | running-config | trace | ping | commit |
|---|---|---|---|---|---|---|
| R1 | show | log | run | trace | ping | - |
| R2 | show | log | run | trace | - | commit |
| R3 | show | log | run | trace | - | commit |
STEP 7: Bring R3 LAN back and set hello-interval 5 level 1 on R1 LAN
| Router | show | syslog | running-config | trace | ping | commit |
|---|---|---|---|---|---|---|
| R1 | show | log | run | trace | ping | commit |
| R2 | show | log | run | trace | - | - |
| R3 | show | log | run | trace | - | commit |
STEP 8: Revert R1 (final state)
| Router | show | syslog | running-config | trace | ping | commit |
|---|---|---|---|---|---|---|
| R1 | show | log | run | trace | ping | commit |
| R2 | show | log | run | trace | - | - |
| R3 | show | log | run | trace | - | - |
Packet captures were taken per STEP on R1 - R2 (point-to-point) and R1 - LAN-SW (LAN). They show IIH timestamps and the Holding Time field.
| STEP | R1 - R2 (P2P) | R1 - LAN-SW (LAN) |
|---|---|---|
| 0 | pcap | pcap |
| 1 | pcap | pcap |
| 2 | pcap | pcap |
| 3 | pcap | pcap |
| 4 | pcap | pcap |
| 5 | pcap | pcap |
| 6 | pcap | pcap |
| 7 | pcap | pcap |
| 8 | pcap | pcap |
Help taken beforehand in a candidate configuration and discarded with abort (nothing committed), and the DIS R3 beforehand: R1 help, R3 interface and trace
References
| Standard | Title | Summary |
|---|---|---|
| ISO/IEC 10589:2002 (2nd edition) | Intermediate System to Intermediate System intra-domain routeing information exchange protocol | Section 8.2.4 covers sending point-to-point IIHs, sections 8.2.6 and 8.4.2.5.2 monitoring adjacencies with the received Holding Time, section 8.4.4 sending LAN IIHs and the DIS dRISISHelloTimer, section 10.1 jitter, table 2 ISISHoldingMultiplier and Jitter, and the annex the defaults of iSISHelloTimer (3 s) and dRISISHelloTimer (1 s). |
| Routing Command Reference for Cisco ASR 9000 Series Routers, IOS XR Release 6.6.x - IS-IS Commands | hello-interval / hello-multiplier | Describes IOS XR hello-interval (default 10 s, level for LANs, a single hello on point-to-point) and hello-multiplier (default 3, the advertised hold time). |
| Cisco IOS IP Routing: ISIS Command Reference - A through I | isis hello-interval | Describes that DIS interfaces use one third of the configured value (for IOS). |
Related articles
- What Is IS-IS
- IS-IS NSAP Addresses and the NET (System ID)
- IS-IS Level 1 and Level 2 (the hierarchy)
- IS-IS Packet Types and Header Format
- IS-IS Adjacency Formation and States
- IS-IS DIS and the Pseudonode
- IS-IS Network Types (broadcast / point-to-point)
- IS-IS Metrics (narrow and wide)
- IS-IS Authentication (hello-password and lsp-password)
- IS-IS LSPs and the Link-State Database
- The Main IS-IS TLVs
- IS-IS Flooding and LSDB Synchronisation
- IS-IS SPF Computation and Route Selection
- The IS-IS ATT Bit and the Level 1 Default Route
- IS-IS Route Leaking and the Up/Down Bit
- IS-IS Route Summarization
- The IS-IS Overload Bit
- IS-IS Hello and Holding Time
- IS-IS Convergence Timers (SPF / LSP Generation)
- IS-IS Redistribution (connected / static)
- IS-IS Redistribution of BGP Routes