Posted on Tuesday, 23rd March 2004 by sean
Since I’ve been having so much fun with IS-IS recently, I thought I’d look closer at the hello process whereby neighbours form an adjacency. I took two routers, connected over an Ethernet interface, and turned on IS-IS.
r0: interface Loopback99 ip address 1.1.1.1 255.255.255.255 ip router isis interface Ethernet0 ip address 10.50.0.1 255.255.255.0 ip router isis router isis net 49.0001.0100.5000.0001.00 is-type level-1
r1:
interface Ethernet0 ip address 10.50.0.3 255.255.255.0 ip router isis router isis net 49.0001.0100.5000.0002.00 is-type level-1
r1#debug isis adj-packets IS-IS Adjacency related packets debugging is on 00:06:57: ISIS-Adj: Rec L1 IIH from 0060.5cf3.bb1e (Ethernet0), cir type L1, cir id 0100.5000.0001.01, length 1497 00:06:59: ISIS-Adj: L1 adj count 0 00:06:59: ISIS-Adj: Run level-1 DR election for Ethernet0 00:06:59: ISIS-Adj: No adjacencies found 00:07:00: ISIS-Adj: Rec L1 IIH from 0060.5cf3.bb1e (Ethernet0), cir type L1, cir id 0100.5000.0001.01, length 1497 00:07:00: ISIS-Adj: New adjacency, level 1 for 0060.5cf3.bb1e 00:07:00: ISIS-Adj: Sending L1 LAN IIH on Ethernet0, length 1497 00:07:03: ISIS-Adj: Rec L1 IIH from 0060.5cf3.bb1e (Ethernet0), cir type L1, cir id 0100.5000.0001.01, length 1497 00:07:03: ISIS-Adj: L1 adj count 1 00:07:03: ISIS-Adj: Adjacency state goes to Up 00:07:03: ISIS-Adj: Run level-1 DR election for Ethernet0 00:07:03: ISIS-Adj: New level-1 DR 0100.5000.0001 on Ethernet0 00:07:03: ISIS-Adj: Sending L1 LAN IIH on Ethernet0, length 1497 00:07:06: ISIS-Adj: Rec L1 IIH from 0060.5cf3.bb1e (Ethernet0), cir type L1, cir id 0100.5000.0001.01, length 1497 00:07:09: ISIS-Adj: Rec L1 IIH from 0060.5cf3.bb1e (Ethernet0), cir type L1, cir id 0100.5000.0001.01, length 1497 00:07:12: ISIS-Adj: Sending L1 LAN IIH on Ethernet0, length 1497 00:07:12: ISIS-Adj: Rec L1 IIH from 0060.5cf3.bb1e (Ethernet0), cir type L1, cir id 0100.5000.0001.01, length 1497 00:07:16: ISIS-Adj: Rec L1 IIH from 0060.5cf3.bb1e (Ethernet0), cir type L1, cir id 0100.5000.0001.01, length 1497
Here, I’ve assigned both hosts a NET in the same area (49.0001). Debugging from R1, I see the IIH coming from R0. The adjacency is then formed, the routers hold a DR election and R0 is chosen as the designated router based on the lower ID (from the NET).
I can then see the loopback route:
r1#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
...
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
...
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
i L1 1.1.1.1 [115/20] via 10.50.0.1, Ethernet0
10.0.0.0/24 is subnetted, 1 subnets
C 10.50.0.0 is directly connected, Ethernet0
What happens if the routers are in different areas?
r0(config)#router isis r0(config-router)#no net 49.0001.0100.5000.0001.00 r0(config-router)#net 49.0002.0100.5000.0001.00
R1:
02:34:21: ISIS-Adj: No adjacencies found 02:34:21: ISIS-Adj: Rec L1 IIH from 0060.5cf3.bb1e (Ethernet0), cir type L1, cir id 0100.5000.0001.01, length 1497 02:34:21: ISIS-Adj: Area mismatch, level 1 IIH on Ethernet0 02:34:21: ISIS-Adj: Sending L1 LAN IIH on Ethernet0, length 1497 02:34:29: ISIS-Adj: Sending L1 LAN IIH on Ethernet0, length 1497 02:34:30: ISIS-Adj: Rec L1 IIH from 0060.5cf3.bb1e (Ethernet0), cir type L1, cir id 0100.5000.0001.01, length 1497 02:34:30: ISIS-Adj: Area mismatch, level 1 IIH on Ethernet0
And then, make both L1-L2 routers:
02:37:24: ISIS-Adj: New adjacency, level 1 & 2 for 0060.5cf3.bb1e 02:37:25: %SYS-5-CONFIG_I: Configured from console by vty0 (10.50.0.253) 02:37:25: ISIS-Adj: Sending L2 LAN IIH on Ethernet0, length 1497 02:37:25: ISIS-Adj: Rec L2 IIH from 0060.5cf3.bb1e (Ethernet0), cir type L1L2, cir id 0100.5000.0001.01, length 1497 02:37:25: ISIS-Adj: L1 adj count 1 02:37:25: ISIS-Adj: L2 adj count 1 02:37:25: ISIS-Adj: Adjacency state goes to Up 02:37:25: ISIS-Adj: Run level-1 DR election for Ethernet0 02:37:25: ISIS-Adj: No change 02:37:25: ISIS-Adj: Run level-2 DR election for Ethernet0 02:37:25: ISIS-Adj: New level-2 DR 0100.5000.0001 on Ethernet0 02:37:26: ISIS-Adj: Sending L2 LAN IIH on Ethernet0, length 1497 02:37:27: ISIS-Adj: Rec L1 IIH from 0060.5cf3.bb1e (Ethernet0), cir type L1L2, cir id 0100.5000.0001.01, length 1497 02:37:28: ISIS-Adj: Rec L2 IIH from 0060.5cf3.bb1e (Ethernet0), cir type L1L2, cir id 0100.5000.0001.01, length 1497 02:37:29: ISIS-Adj: Rec L1 IIH from 0060.5cf3.bb1e (Ethernet0), cir type L1L2, cir id 0100.5000.0001.01, length 1497 02:37:31: ISIS-Adj: Rec L2 IIH from 0060.5cf3.bb1e (Ethernet0), cir type L1L2, cir id 0100.5000.0001.01, length 1497 02:37:32: ISIS-Adj: Rec L1 IIH from 0060.5cf3.bb1e (Ethernet0), cir type L1L2, cir id 0100.5000.0001.01, length 1497 02:37:33: ISIS-Adj: Sending L1 LAN IIH on Ethernet0, length 1497 02:37:34: ISIS-Adj: Rec L2 IIH from 0060.5cf3.bb1e (Ethernet0), cir type L1L2, cir id 0100.5000.0001.01, length 1497 02:37:35: ISIS-Adj: Sending L2 LAN IIH on Ethernet0, length 1497
Note how both L1 and L2 IIH PDUs are sent and received. There are also separate L1 and L2 elections and tables:
r1#show isis database IS-IS Level-1 Link State Database: LSPID LSP Seq Num LSP Checksum LSP Holdtime ATT/P/OL r0.00-00 0x0000006A 0x9F67 1158 0/0/0 r0.01-00 0x00000010 0x6AE4 1159 0/0/0 r1.00-00 * 0x00000014 0x9823 1160 0/0/0 IS-IS Level-2 Link State Database: LSPID LSP Seq Num LSP Checksum LSP Holdtime ATT/P/OL r0.00-00 0x00000002 0x224D 1162 0/0/0 r0.01-00 0x00000001 0x18CE 1158 0/0/0 r1.00-00 * 0x00000002 0xBF68 1164 0/0/0 r1#show isis topology IS-IS paths to level-1 routers System Id Metric Next-Hop Interface SNPA r0 10 r0 Et0 0060.5cf3.bb1e r1 -- IS-IS paths to level-2 routers System Id Metric Next-Hop Interface SNPA r0 10 r0 Et0 0060.5cf3.bb1e r1
Jacking up the debug level to see the LSP exchange (back into L1-L1 mode)
r1# show debug CLNS: IS-IS Adjacency related packets debugging is on IS-IS SPF events debugging is on IS-IS Update related packet debugging is on IS-IS SPF triggering events debugging is on IS-IS local updates debugging is on r1# clear isis * 00:15:38: ISIS-Adj: Rec L1 IIH from 0060.5cf3.bb1e (Ethernet0), cir type L1, cir id 0100.5000.0001.01, length 1497 00:15:39: ISIS-Adj: Sending L1 LAN IIH on Ethernet0, length 1497 r1# 00:15:40: ISIS-Spf: Aging L1 LSP 3 (0100.5000.0001.00-00), version 10 00:15:40: ISIS-Spf: Aging IP 1.1.1.1/255.255.255.255, next hop 10.50.0.1 00:15:40: ISIS-Spf: Deleted NDB 00:15:40: ISIS-Spf: Aging L1 LSP 1 (0100.5000.0002.00-00), version 10 00:15:40: ISIS-Spf: Aging L1 LSP 2 (0100.5000.0001.01-00), version 10 00:15:40: ISIS-Adj: L1 adj count 0 00:15:40: ISIS-Spf: L1 SPF needed, database changed, from 0x388860C 00:15:40: ISIS-Adj: Run level-1 DR election for Ethernet0 00:15:40: ISIS-Adj: No adjacencies found 00:15:41: ISIS-Upd: Building L1 LSP 00:15:41: ISIS-Upd: New LSP 00:15:41: ISIS-Spf: L1, new LSP 0 0100.5000.0002.00-00 00:15:41: ISIS-Upd: Full SPF required 00:15:41: ISIS-Adj: Rec L1 IIH from 0060.5cf3.bb1e (Ethernet0), cir type L1, cir id 0100.5000.0001.01, length 1497 00:15:41: ISIS-Adj: New adjacency, level 1 for 0060.5cf3.bb1e 00:15:41: ISIS-Adj: Sending L1 LAN IIH on Ethernet0, length 1497 00:15:44: ISIS-Adj: Rec L1 IIH from 0060.5cf3.bb1e (Ethernet0), cir type L1, cir id 0100.5000.0001.01, length 1497 00:15:44: ISIS-Spf: L1 SPF needed, new adjacency, from 0x388DBAE 00:15:44: ISIS-Loc: L1 DR changed from 0x388DBBE 00:15:44: ISIS-Adj: L1 adj count 1 00:15:44: ISIS-Adj: Adjacency state goes to Up 00:15:44: ISIS-Adj: Run level-1 DR election for Ethernet0 00:15:44: ISIS-Adj: New level-1 DR 0100.5000.0001 on Ethernet0 00:15:44: ISIS-Adj: Sending L1 LAN IIH on Ethernet0, length 1497 00:15:46: ISIS-Upd: Building L1 LSP 00:15:46: ISIS-Upd: TLV contents different, code 2 00:15:46: ISIS-Spf: L1, 0100.5000.0002.00-00 TLV contents changed, code 2 00:15:46: ISIS-Upd: Full SPF required 00:15:46: ISIS-Upd: Sending L1 LSP 0100.5000.0002.00-00, seq 2, ht 1199 on Ethernet0 00:15:46: ISIS-Upd: Rec L1 LSP 0100.5000.0002.00-00, seq 6, ht 677, 00:15:46: ISIS-Upd: from SNPA 0060.5cf3.bb1e (Ethernet0) 00:15:46: ISIS-Upd: LSP newer than database copy 00:15:46: ISIS-Loc: L1 regeneration 00:15:46: ISIS-Upd: Building L1 LSP 00:15:46: ISIS-Upd: No change 00:15:46: ISIS-Upd: Regenerated LSP 00:15:46: ISIS-Upd: Sending L1 LSP 0100.5000.0002.00-00, seq 7, ht 1199 on Ethernet0 00:15:46: ISIS-Spf: Compute L1 SPT 00:15:46: ISIS-Spf: Move 0100.5000.0002.00-00 to PATHS, metric 0 00:15:46: ISIS-Spf: Aging L1 LSP 1 (deleted), version 11 00:15:46: ISIS-Spf: Aging L1 LSP 2 (deleted), version 11 00:15:46: ISIS-Spf: Aging L1 LSP 3 (deleted), version 11 00:15:46: ISIS-Spf: Aging L1 LSP 4 (0100.5000.0002.00-00), version 8 00:15:47: ISIS-Adj: Rec L1 IIH from 0060.5cf3.bb1e (Ethernet0), cir type L1, cir id 0100.5000.0001.01, length 1497 00:15:48: ISIS-Upd: Rec L1 LSP 0100.5000.0001.00-00, seq 5D, ht 751, 00:15:48: ISIS-Upd: from SNPA 0060.5cf3.bb1e (Ethernet0) 00:15:48: ISIS-Upd: LSP newer than database copy 00:15:48: ISIS-Upd: TLV contents different, code 1 00:15:48: ISIS-Upd: TLV contents different, code 129 00:15:48: ISIS-Upd: TLV contents different, code 137 00:15:48: ISIS-Upd: TLV contents different, code 132 00:15:48: ISIS-Upd: TLV contents different, code 128 00:15:48: ISIS-Upd: TLV contents different, code 2 00:15:48: ISIS-Spf: L1, 0100.5000.0001.00-00 TLV contents changed, code 2 00:15:48: ISIS-Upd: Full SPF required 00:15:48: ISIS-Upd: Rec L1 LSP 0100.5000.0001.01-00, seq 3, ht 608, 00:15:48: ISIS-Upd: from SNPA 0060.5cf3.bb1e (Ethernet0) 00:15:48: ISIS-Upd: LSP newer than database copy 00:15:48: ISIS-Upd: TLV contents different, code 2 00:15:48: ISIS-Spf: L1, 0100.5000.0001.01-00 TLV contents changed, code 2 00:15:48: ISIS-Upd: Full SPF required 00:15:50: ISIS-Adj: Rec L1 IIH from 0060.5cf3.bb1e (Ethernet0), cir type L1, cir id 0100.5000.0001.01, length 1497 00:15:52: ISIS-Spf: Compute L1 SPT 00:15:52: ISIS-Spf: Move 0100.5000.0002.00-00 to PATHS, metric 0 00:15:52: ISIS-Spf: Add 0100.5000.0001.01-00 to TENT, metric 10 00:15:52: ISIS-Spf: Move 0100.5000.0001.01-00 to PATHS, metric 10 00:15:52: ISIS-Spf: considering adj to 0100.5000.0001 (Ethernet0) metric 10, level 1, circuit 3, adj 1 00:15:52: ISIS-Spf: (accepted) 00:15:52: ISIS-Spf: Add 0100.5000.0001.00-00 to TENT, metric 10 00:15:52: ISIS-Spf: Next hop 0100.5000.0001 (Ethernet0) 00:15:52: ISIS-Spf: Move 0100.5000.0001.00-00 to PATHS, metric 10 00:15:52: ISIS-Spf: Add 10.50.0.0/255.255.255.0 to IP RIB, metric 20 00:15:52: ISIS-Spf: Next hop 0100.5000.0001/10.50.0.1 (Ethernet0) (rejected) 00:15:52: ISIS-Spf: Add 1.1.1.1/255.255.255.255 to IP RIB, metric 20 00:15:52: ISIS-Spf: Next hop 0100.5000.0001/10.50.0.1 (Ethernet0) (accepted) 00:15:52: ISIS-Spf: Aging L1 LSP 1 (0100.5000.0001.01-00), version 13 00:15:52: ISIS-Spf: Aging L1 LSP 2 (0100.5000.0001.00-00), version 13 00:15:52: ISIS-Spf: Aging L1 LSP 4 (0100.5000.0002.00-00), version 9 00:15:53: ISIS-Adj: Rec L1 IIH from 0060.5cf3.bb1e (Ethernet0), cir type L1, cir id 0100.5000.0001.01, length 1497 00:15:53: ISIS-Adj: Sending L1 LAN IIH on Ethernet0, length 1497 00:15:55: ISIS-Adj: Rec L1 IIH from 0060.5cf3.bb1e (Ethernet0), cir type L1, cir id 0100.5000.0001.01, length 1497 00:15:58: ISIS-Adj: Rec L1 IIH from 0060.5cf3.bb1e (Ethernet0), cir type L1, cir id 0100.5000.0001.01, length 1497 00:16:01: ISIS-Adj: Sending L1 LAN IIH on Ethernet0, length 1497 00:16:01: ISIS-Adj: Rec L1 IIH from 0060.5cf3.bb1e (Ethernet0), cir type L1, cir id 0100.5000.0001.01, length 1497und all All possible debugging has been turned off 00:16:04: ISIS-Adj: Rec L1 IIH from 0060.5cf3.bb1e (Ethernet0), cir type L1, cir id 0100.5000.0001.01, length 1497 r1#show isis database IS-IS Level-1 Link State Database: LSPID LSP Seq Num LSP Checksum LSP Holdtime ATT/P/OL r0.00-00 0x0000005D 0xB75E 687 0/0/0 r0.01-00 0x00000003 0x82DB 544 0/0/0 r1.00-00 * 0x00000007 0xB01A 1134 0/0/0 r1#show isis topology IS-IS paths to level-1 routers System Id Metric Next-Hop Interface SNPA r0 10 r0 Et0 0060.5cf3.bb1e r1
No related posts.
Related posts brought to you by Yet Another Related Posts Plugin.
Posted in Routing | Comments (0)
