IS-IS no network migration from level-1 to level-2 database

swenr · August 29, 2023, 9:10am

Hello VyOS forum,
on router V2 the migration from the 10.10.10.0/24 network from the level-1 database to the level-2 database is not done.
The same on V4 for the 20.20.20.0/24 network from V3.

Topology and commands:

vyos@Vx:~$ sh version
Version: VyOS 1.4-rolling-202308280021
Release train: current

Built by: autobuild@vyos.net
Built on: Mon 28 Aug 2023 00:23 UTC
Build UUID: 2f75cb27-26e9-4724-8212-acbe0f0547ce
Build commit ID: ac5a48ecda2880

Architecture: x86_64
Boot via: installed image
System type: KVM guest

Hardware vendor: QEMU
Hardware model: Standard PC (i440FX + PIIX, 1996)
Hardware S/N:
Hardware UUID: afa3c146-909a-46d0-a5f0-180d210f186c

Copyright: VyOS maintainers and contributors
vyos@Vx:~$

V1:
vyos@V1:~$ sh configuration commands
set interfaces ethernet eth0 address ‘192.168.12.1/24’
set interfaces ethernet eth3 address ‘10.10.10.1/24’
set protocols isis interface eth0
set protocols isis interface eth3 passive
set protocols isis level ‘level-1’
set protocols isis net ‘49.0012.0000.0000.0001.00’
set system host-name ‘V1’

vyos@V1:~$ sh isis database detail
Area VyOS:
IS-IS Level-1 link-state database:
LSP ID PduLen SeqNumber Chksum Holdtime ATT/P/OL
V1.00-00 * 93 0x00000003 0xd640 1145 0/0/0
Protocols Supported: IPv4, IPv6
Area Address: 49.0012
Hostname: V1
TE Router ID: 192.168.12.1
Router Capability: 192.168.12.1 , D:0, S:0
Extended Reachability: 0000.0000.0001.02 (Metric: 10)
IPv4 Interface Address: 192.168.12.1
Extended IP Reachability: 192.168.12.0/24 (Metric: 10)
Subtlvs:
Extended IP Reachability: 10.10.10.0/24 (Metric: 10)
Subtlvs:

V1.02-00 * 51 0x00000001 0x8843 1138 0/0/0
Extended Reachability: 0000.0000.0001.00 (Metric: 0)
Extended Reachability: 0000.0000.0002.00 (Metric: 0)

V2.00-00 93 0x00000003 0x3c44 1136 1/0/0
Protocols Supported: IPv4, IPv6
Area Address: 49.0012
Hostname: V2
TE Router ID: 192.168.24.2
Router Capability: 192.168.24.2 , D:0, S:0
Extended Reachability: 0000.0000.0001.02 (Metric: 10)
IPv4 Interface Address: 192.168.24.2
Extended IP Reachability: 192.168.12.0/24 (Metric: 10)
Extended IP Reachability: 192.168.24.0/24 (Metric: 10)

3 LSPs

V2:
vyos@V2:~$ sh conf commands
set interfaces ethernet eth0 address ‘192.168.12.2/24’
set interfaces ethernet eth3 address ‘192.168.24.2/24’
set protocols isis interface eth0
set protocols isis interface eth3
set protocols isis level ‘level-1-2’
set protocols isis net ‘49.0012.0000.0000.0002.00’
set system host-name ‘V2’

vyos@V2:~$ sh isis database d
Area VyOS:
IS-IS Level-1 link-state database:
LSP ID PduLen SeqNumber Chksum Holdtime ATT/P/OL
V1.00-00 93 0x00000003 0xd640 1014 0/0/0
Protocols Supported: IPv4, IPv6
Area Address: 49.0012
Hostname: V1
TE Router ID: 192.168.12.1
Router Capability: 192.168.12.1 , D:0, S:0
Extended Reachability: 0000.0000.0001.02 (Metric: 10)
IPv4 Interface Address: 192.168.12.1
Extended IP Reachability: 192.168.12.0/24 (Metric: 10)
Extended IP Reachability: 10.10.10.0/24 (Metric: 10)

V1.02-00 51 0x00000001 0x8843 1007 0/0/0
Extended Reachability: 0000.0000.0001.00 (Metric: 0)
Extended Reachability: 0000.0000.0002.00 (Metric: 0)

V2.00-00 * 93 0x00000003 0x3c44 1005 1/0/0
Protocols Supported: IPv4, IPv6
Area Address: 49.0012
Hostname: V2
TE Router ID: 192.168.24.2
Router Capability: 192.168.24.2 , D:0, S:0
Extended Reachability: 0000.0000.0001.02 (Metric: 10)
IPv4 Interface Address: 192.168.24.2
Extended IP Reachability: 192.168.12.0/24 (Metric: 10)
Subtlvs:
Extended IP Reachability: 192.168.24.0/24 (Metric: 10)
Subtlvs:

3 LSPs

IS-IS Level-2 link-state database:
LSP ID PduLen SeqNumber Chksum Holdtime ATT/P/OL
V2.00-00 * 93 0x00000011 0xf380 1030 0/0/0
Protocols Supported: IPv4, IPv6
Area Address: 49.0012
Hostname: V2
TE Router ID: 192.168.24.2
Router Capability: 192.168.24.2 , D:0, S:0
Extended Reachability: 0000.0000.0004.05 (Metric: 10)
IPv4 Interface Address: 192.168.24.2
Extended IP Reachability: 192.168.12.0/24 (Metric: 10)
Subtlvs:
Extended IP Reachability: 192.168.24.0/24 (Metric: 10)
Subtlvs:

V4.00-00 93 0x00000011 0x0a10 984 0/0/0
Protocols Supported: IPv4, IPv6
Area Address: 49.0034
Hostname: V4
TE Router ID: 192.168.34.2
Router Capability: 192.168.34.2 , D:0, S:0
Extended Reachability: 0000.0000.0004.05 (Metric: 10)
IPv4 Interface Address: 192.168.34.2
Extended IP Reachability: 192.168.34.0/24 (Metric: 10)
Extended IP Reachability: 192.168.24.0/24 (Metric: 10)

V4.05-00 51 0x00000006 0x6e4d 979 0/0/0
Extended Reachability: 0000.0000.0004.00 (Metric: 0)
Extended Reachability: 0000.0000.0002.00 (Metric: 0)

3 LSPs

vyos@V2:~$

The 10.10.10.0/24 network in clearly in the level-1 database on V2, but not in the level-2 database.
It’s an issue in FRR, (I think):
vyos@V2:~$ vtysh

V2# sh isis database detail
Area VyOS:
IS-IS Level-1 link-state database:
LSP ID PduLen SeqNumber Chksum Holdtime ATT/P/OL
V1.00-00 93 0x00000003 0xd640 930 0/0/0
Protocols Supported: IPv4, IPv6
Area Address: 49.0012
Hostname: V1
TE Router ID: 192.168.12.1
Router Capability: 192.168.12.1 , D:0, S:0
Extended Reachability: 0000.0000.0001.02 (Metric: 10)
IPv4 Interface Address: 192.168.12.1
Extended IP Reachability: 192.168.12.0/24 (Metric: 10)
Extended IP Reachability: 10.10.10.0/24 (Metric: 10)

V1.02-00 51 0x00000001 0x8843 923 0/0/0
Extended Reachability: 0000.0000.0001.00 (Metric: 0)
Extended Reachability: 0000.0000.0002.00 (Metric: 0)

V2.00-00 * 93 0x00000003 0x3c44 921 1/0/0
Protocols Supported: IPv4, IPv6
Area Address: 49.0012
Hostname: V2
TE Router ID: 192.168.24.2
Router Capability: 192.168.24.2 , D:0, S:0
Extended Reachability: 0000.0000.0001.02 (Metric: 10)
IPv4 Interface Address: 192.168.24.2
Extended IP Reachability: 192.168.12.0/24 (Metric: 10)
Subtlvs:
Extended IP Reachability: 192.168.24.0/24 (Metric: 10)
Subtlvs:

3 LSPs

IS-IS Level-2 link-state database:
LSP ID PduLen SeqNumber Chksum Holdtime ATT/P/OL
V2.00-00 * 93 0x00000011 0xf380 946 0/0/0
Protocols Supported: IPv4, IPv6
Area Address: 49.0012
Hostname: V2
TE Router ID: 192.168.24.2
Router Capability: 192.168.24.2 , D:0, S:0
Extended Reachability: 0000.0000.0004.05 (Metric: 10)
IPv4 Interface Address: 192.168.24.2
Extended IP Reachability: 192.168.12.0/24 (Metric: 10)
Subtlvs:
Extended IP Reachability: 192.168.24.0/24 (Metric: 10)
Subtlvs:

V4.00-00 93 0x00000011 0x0a10 900 0/0/0
Protocols Supported: IPv4, IPv6
Area Address: 49.0034
Hostname: V4
TE Router ID: 192.168.34.2
Router Capability: 192.168.34.2 , D:0, S:0
Extended Reachability: 0000.0000.0004.05 (Metric: 10)
IPv4 Interface Address: 192.168.34.2
Extended IP Reachability: 192.168.34.0/24 (Metric: 10)
Extended IP Reachability: 192.168.24.0/24 (Metric: 10)

V4.05-00 51 0x00000006 0x6e4d 895 0/0/0
Extended Reachability: 0000.0000.0004.00 (Metric: 0)
Extended Reachability: 0000.0000.0002.00 (Metric: 0)

3 LSPs

V2#

It’s in the routing table of V2:
vyos@V2:~$ sh ip route
Codes: K - kernel route, C - connected, S - static, R - RIP,
O - OSPF, I - IS-IS, B - BGP, E - EIGRP, N - NHRP,
T - Table, v - VNC, V - VNC-Direct, A - Babel, F - PBR,
f - OpenFabric,
> - selected route, * - FIB route, q - queued, r - rejected, b - backup
t - trapped, o - offload failure

I>* 10.10.10.0/24 [115/20] via 192.168.12.1, eth0, weight 1, 00:07:55
I 192.168.12.0/24 [115/20] via 192.168.12.1, eth0 inactive, weight 1, 00:07:44
C>* 192.168.12.0/24 is directly connected, eth0, 00:08:27
C>* 192.168.24.0/24 is directly connected, eth3, 00:08:27
I>* 192.168.34.0/24 [115/20] via 192.168.24.1, eth3, weight 1, 00:07:55
vyos@V2:~$

But it’s not forwarded to V4 …
vyos@V4:~$ sh ip route
Codes: K - kernel route, C - connected, S - static, R - RIP,
O - OSPF, I - IS-IS, B - BGP, E - EIGRP, N - NHRP,
T - Table, v - VNC, V - VNC-Direct, A - Babel, F - PBR,
f - OpenFabric,
> - selected route, * - FIB route, q - queued, r - rejected, b - backup
t - trapped, o - offload failure

I>* 20.20.20.0/24 [115/20] via 192.168.34.1, eth0, weight 1, 00:44:40
I>* 192.168.12.0/24 [115/20] via 192.168.24.2, eth3, weight 1, 00:09:01
C>* 192.168.24.0/24 is directly connected, eth3, 00:57:23
I 192.168.34.0/24 [115/20] via 192.168.34.1, eth0 inactive, weight 1, 00:01:30
C>* 192.168.34.0/24 is directly connected, eth0, 00:49:31
vyos@V4:~$

swenr · August 29, 2023, 10:52am

Even when using “set protocols isis metric-style wide” it is not working.

Cheeze_It · August 30, 2023, 7:28pm

I am showing this behavior too. I have 4 routers connected in a somewhat similar setup and I am seeing the same. The edge routers can’t see each other, and the backbone routers can’t see the edge router of the “other side” either:

vyos@VYOS-EDGE-LEFT:~$ show isis database
Area VyOS:
IS-IS Level-1 link-state database:
LSP ID                  PduLen  SeqNumber   Chksum  Holdtime  ATT/P/OL
VYOS-BB-LEFT.00-00        105   0x00000005  0x67d1     720    1/0/0
VYOS-EDGE-LEFT.00-00 *    107   0x00000005  0xc8e3     761    0/0/0
VYOS-EDGE-LEFT.02-00 *     51   0x00000002  0xe59b     761    0/0/0
    3 LSPs

vyos@VYOS-EDGE-RIGHT:~$ show isis database
Area VyOS:
IS-IS Level-1 link-state database:
LSP ID                  PduLen  SeqNumber   Chksum  Holdtime  ATT/P/OL
VYOS-EDGE-RIGH.00-00 *    108   0x00000005  0x1650     789    0/0/0
VYOS-EDGE-RIGH.02-00 *     51   0x00000002  0xceb9     787    0/0/0
VYOS-BB-RIGHT.00-00       106   0x00000005  0x03e4     743    1/0/0
    3 LSPs

vyos@VYOS-BB-LEFT:~$ show isis database
Area VyOS:
IS-IS Level-1 link-state database:
LSP ID                  PduLen  SeqNumber   Chksum  Holdtime  ATT/P/OL
VYOS-BB-LEFT.00-00   *    105   0x00000005  0x67d1     714    1/0/0
VYOS-EDGE-LEFT.00-00      107   0x00000005  0xc8e3     755    0/0/0
VYOS-EDGE-LEFT.02-00       51   0x00000002  0xe59b     755    0/0/0
    3 LSPs

IS-IS Level-2 link-state database:
LSP ID                  PduLen  SeqNumber   Chksum  Holdtime  ATT/P/OL
VYOS-BB-RIGHT.00-00       106   0x00000005  0x8963     712    0/0/0
VYOS-BB-LEFT.00-00   *    105   0x00000005  0x60e0     716    0/0/0
VYOS-BB-LEFT.03-00   *     51   0x00000002  0xcbb5     906    0/0/0
    3 LSPs

vyos@VYOS-BB-RIGHT:~$ show isis database
Area VyOS:
IS-IS Level-1 link-state database:
LSP ID                  PduLen  SeqNumber   Chksum  Holdtime  ATT/P/OL
VYOS-EDGE-RIGH.00-00      108   0x00000005  0x1650     787    0/0/0
VYOS-EDGE-RIGH.02-00       51   0x00000002  0xceb9     785    0/0/0
VYOS-BB-RIGHT.00-00  *    106   0x00000005  0x03e4     741    1/0/0
    3 LSPs

IS-IS Level-2 link-state database:
LSP ID                  PduLen  SeqNumber   Chksum  Holdtime  ATT/P/OL
VYOS-BB-RIGHT.00-00  *    106   0x00000005  0x8963     710    0/0/0
VYOS-BB-LEFT.00-00        105   0x00000005  0x60e0     715    0/0/0
VYOS-BB-LEFT.03-00         51   0x00000002  0xcbb5     904    0/0/0
    3 LSPs

Cheeze_It · August 30, 2023, 7:28pm

I asked the FRR developers if this is expected behavior…and how to get around it.

fernando · August 30, 2023, 9:33pm

this a normal behavior in ISIS , Level-1 route can’t see level-2 route for that reason exits ABR which belong L1/L2 process , try to set the attached-bit or redistribute L2 into L1 on ABR :

https://docs.vyos.io/en/latest/configuration/protocols/isis.html#cfgcmd-set-protocols-isis-set-attached-bit

Cheeze_It · August 30, 2023, 10:21pm

So this actually is not normal behavior in IS-IS if you consider other vendors. This is why I asked the FRR developers on the behavior. L1 → L2 is normal behavior, and the attached bit gives a default route. But that only works technically if you’re attached to another area. Not sure if FRR does that part like that either. That’s why this question is coming up.

Cisco: Configure IS-IS Adjacency and Area Types. - Cisco

By default, the L1/L2 router allows one way passage of prefixes from L1 Area to L2 Area, but not in reverse.

Juniper: Example: Configuring IS-IS Route Leaking from a Level 2 Area to a Level 1 Area | Junos OS | Juniper Networks

By default, IS-IS protocol leaks routing information from a Level 1 area to a Level 2 area. However, to leak routing information from a Level 2 area to a Level 1 area, an export policy must be explicitly configured.

fernando · August 30, 2023, 11:33pm

I got it , I misunderstood the behavior , as you mentioned it’s possible that has a different default behavior .Although , it may be redistribution from Level1 into Level2 and vice versa , it works as expected .

fernando · August 31, 2023, 3:39pm

it seems this feature doesn’t work on FRR , at least , l1/l2 are not able to redistribute L1 into L2 which is expected beheivor :

github.com/FRRouting/frr

ISIS: The L1-2 router cannot advertise L1 routes into L2.

opened 02:31AM - 11 Feb 23 UTC

MintLife619

isis

ISIS L1-2 router with FRR installed cannot advertise the route from Level-1 to L…evel-2 [√] Did you check if this is a duplicate issue? [√] Did you test it on the latest FRRouting/frr master branch? **To Reproduce** Steps to reproduce the behavior: &emsp;&emsp;1. Virtual bridges are used to connect containers with frr to form a network. &emsp;&emsp;2. Open the ISIS daemon in the container (router) where the ISIS protocol needs to be deployed. &emsp;&emsp;3. Configure the protocol. The interface connected with L1 domain is set as "isis circuit-type level-1" and the interface connected with L2 domain is set as "isis circuit-type level-2". &emsp;&emsp;4. Perform connectivity test. **Expected behavior** Different ISIS regions should be able to connect with each other. **Versions** * OS Version: Ubuntu 20.04 LTS * LXD/LXC Version: 5.10. Routers are Linux containers running FRR. * Kernel: 5.4.0-135-generic * FRR Version: 8.4.2 **Additional context** The Network topology diagram: AR1(L1) --- AR2(L1/2) --- AR3(L2) --- AR4(L1/2) --- AR5(L1) ![image](https://user-images.githubusercontent.com/61102055/218114997-dc33c12b-4d25-4d7f-994c-cbfc28c13d2d.png) **logs and captures** show running-config: AR1: ``` AR1# show running-config Building configuration... Current configuration: ! frr version 8.4.2 frr defaults traditional hostname AR1 log syslog informational no ipv6 forwarding service integrated-vtysh-config ! interface lo ip address 1.1.1.1/32 ip router isis AA exit ! interface eth0 ip router isis AA exit ! router isis AA is-type level-1 net 49.0002.0000.0000.1111.00 exit ! end ``` AR2: ``` AR2# show running-config Building configuration... Current configuration: ! frr version 8.4.2 frr defaults traditional hostname AR2 log syslog informational no ipv6 forwarding service integrated-vtysh-config ! interface lo ip address 2.2.2.2/32 ip router isis AA exit ! interface eth0 ip router isis AA isis circuit-type level-1 exit ! interface eth1 ip router isis AA isis circuit-type level-2-only exit ! interface loo exit ! router isis AA net 49.0002.0000.0000.2222.00 net 49.0001.0000.0000.2222.00 exit ! end ``` AR3: ``` AR3# show running-config Building configuration... Current configuration: ! frr version 8.4.2 frr defaults traditional hostname AR3 log syslog informational no ipv6 forwarding service integrated-vtysh-config ! interface lo ip address 3.3.3.3/32 ip router isis AA exit ! interface eth0 ip router isis AA exit ! interface eth1 ip router isis AA exit ! router isis AA is-type level-2-only net 49.0001.0000.0000.3333.00 exit ! end ``` AR4 and AR5 are similar to AR1 and AR2. show isis databases: AR1 database: ``` AR1# show isis database detail Area AA: IS-IS Level-1 link-state database: LSP ID PduLen SeqNumber Chksum Holdtime ATT/P/OL AR1.00-00 * 92 0x00000022 0x04fe 366 0/0/0 Protocols Supported: IPv4 Area Address: 49.0002 Hostname: AR1 TE Router ID: 1.1.1.1 Router Capability: 1.1.1.1 , D:0, S:0 Extended Reachability: 0000.0000.2222.46 (Metric: 10) IPv4 Interface Address: 1.1.1.1 Extended IP Reachability: 12.1.1.0/24 (Metric: 10) Extended IP Reachability: 1.1.1.1/32 (Metric: 10) AR2.00-00 104 0x00000022 0x4fe1 1051 1/0/0 Protocols Supported: IPv4 Area Address: 49.0002 Area Address: 49.0001 Hostname: AR2 TE Router ID: 2.2.2.2 Router Capability: 2.2.2.2 , D:0, S:0 Extended Reachability: 0000.0000.2222.46 (Metric: 10) IPv4 Interface Address: 2.2.2.2 Extended IP Reachability: 12.1.1.0/24 (Metric: 10) Extended IP Reachability: 23.1.1.0/24 (Metric: 10) Extended IP Reachability: 2.2.2.2/32 (Metric: 10) AR2.46-00 51 0x00000017 0xf8c7 950 1/0/0 Extended Reachability: 0000.0000.2222.00 (Metric: 0) Extended Reachability: 0000.0000.1111.00 (Metric: 0) 3 LSPs ``` AR2 database: ``` AR2# show isis database detail Area AA: IS-IS Level-1 link-state database: LSP ID PduLen SeqNumber Chksum Holdtime ATT/P/OL AR1.00-00 92 0x00000023 0x02ff 1120 0/0/0 Protocols Supported: IPv4 Area Address: 49.0002 Hostname: AR1 TE Router ID: 1.1.1.1 Router Capability: 1.1.1.1 , D:0, S:0 Extended Reachability: 0000.0000.2222.46 (Metric: 10) IPv4 Interface Address: 1.1.1.1 Extended IP Reachability: 12.1.1.0/24 (Metric: 10) Extended IP Reachability: 1.1.1.1/32 (Metric: 10) AR2.00-00 * 104 0x00000022 0x4fe1 942 1/0/0 Protocols Supported: IPv4 Area Address: 49.0002 Area Address: 49.0001 Hostname: AR2 TE Router ID: 2.2.2.2 Router Capability: 2.2.2.2 , D:0, S:0 Extended Reachability: 0000.0000.2222.46 (Metric: 10) IPv4 Interface Address: 2.2.2.2 Extended IP Reachability: 12.1.1.0/24 (Metric: 10) Extended IP Reachability: 23.1.1.0/24 (Metric: 10) Extended IP Reachability: 2.2.2.2/32 (Metric: 10) AR2.46-00 * 51 0x00000017 0xf8c7 841 1/0/0 Extended Reachability: 0000.0000.2222.00 (Metric: 0) Extended Reachability: 0000.0000.1111.00 (Metric: 0) 3 LSPs IS-IS Level-2 link-state database: LSP ID PduLen SeqNumber Chksum Holdtime ATT/P/OL AR2.00-00 * 104 0x00000021 0x32e1 869 0/0/0 Protocols Supported: IPv4 Area Address: 49.0002 Area Address: 49.0001 Hostname: AR2 TE Router ID: 2.2.2.2 Router Capability: 2.2.2.2 , D:0, S:0 Extended Reachability: 0000.0000.3333.4a (Metric: 10) IPv4 Interface Address: 2.2.2.2 Extended IP Reachability: 12.1.1.0/24 (Metric: 10) Extended IP Reachability: 23.1.1.0/24 (Metric: 10) Extended IP Reachability: 2.2.2.2/32 (Metric: 10) AR3.00-00 111 0x0000001d 0xc66e 1044 0/0/0 Protocols Supported: IPv4 Area Address: 49.0001 Hostname: AR3 TE Router ID: 3.3.3.3 Router Capability: 3.3.3.3 , D:0, S:0 Extended Reachability: 0000.0000.3333.4a (Metric: 10) Extended Reachability: 0000.0000.4444.4e (Metric: 10) IPv4 Interface Address: 3.3.3.3 Extended IP Reachability: 23.1.1.0/24 (Metric: 10) Extended IP Reachability: 34.1.1.0/24 (Metric: 10) Extended IP Reachability: 3.3.3.3/32 (Metric: 10) AR3.4a-00 51 0x00000016 0x70ee 1033 0/0/0 Extended Reachability: 0000.0000.3333.00 (Metric: 0) Extended Reachability: 0000.0000.2222.00 (Metric: 0) AR4.00-00 104 0x0000001c 0x95c9 1050 0/0/0 Protocols Supported: IPv4 Area Address: 49.0003 Area Address: 49.0001 Hostname: AR4 TE Router ID: 4.4.4.4 Router Capability: 4.4.4.4 , D:0, S:0 Extended Reachability: 0000.0000.4444.4e (Metric: 10) IPv4 Interface Address: 4.4.4.4 Extended IP Reachability: 34.1.1.0/24 (Metric: 10) Extended IP Reachability: 45.1.1.0/24 (Metric: 10) Extended IP Reachability: 4.4.4.4/32 (Metric: 10) AR4.4e-00 51 0x00000016 0xed07 1096 0/0/0 Extended Reachability: 0000.0000.4444.00 (Metric: 0) Extended Reachability: 0000.0000.3333.00 (Metric: 0) 5 LSPs ``` AR3 database: ``` AR3# show isis database detail Area AA: IS-IS Level-2 link-state database: LSP ID PduLen SeqNumber Chksum Holdtime ATT/P/OL AR2.00-00 104 0x0000001e 0x38de 520 0/0/0 Protocols Supported: IPv4 Area Address: 49.0002 Area Address: 49.0001 Hostname: AR2 TE Router ID: 2.2.2.2 Router Capability: 2.2.2.2 , D:0, S:0 Extended Reachability: 0000.0000.3333.4a (Metric: 10) IPv4 Interface Address: 2.2.2.2 Extended IP Reachability: 12.1.1.0/24 (Metric: 10) Extended IP Reachability: 23.1.1.0/24 (Metric: 10) Extended IP Reachability: 2.2.2.2/32 (Metric: 10) AR3.00-00 * 111 0x0000001a 0xcc6b 610 0/0/0 Protocols Supported: IPv4 Area Address: 49.0001 Hostname: AR3 TE Router ID: 3.3.3.3 Router Capability: 3.3.3.3 , D:0, S:0 Extended Reachability: 0000.0000.3333.4a (Metric: 10) Extended Reachability: 0000.0000.4444.4e (Metric: 10) IPv4 Interface Address: 3.3.3.3 Extended IP Reachability: 23.1.1.0/24 (Metric: 10) Extended IP Reachability: 34.1.1.0/24 (Metric: 10) Extended IP Reachability: 3.3.3.3/32 (Metric: 10) AR3.4a-00 * 51 0x00000013 0x76eb 656 0/0/0 Extended Reachability: 0000.0000.3333.00 (Metric: 0) Extended Reachability: 0000.0000.2222.00 (Metric: 0) AR4.00-00 104 0x00000019 0x9bc6 661 0/0/0 Protocols Supported: IPv4 Area Address: 49.0003 Area Address: 49.0001 Hostname: AR4 TE Router ID: 4.4.4.4 Router Capability: 4.4.4.4 , D:0, S:0 Extended Reachability: 0000.0000.4444.4e (Metric: 10) IPv4 Interface Address: 4.4.4.4 Extended IP Reachability: 34.1.1.0/24 (Metric: 10) Extended IP Reachability: 45.1.1.0/24 (Metric: 10) Extended IP Reachability: 4.4.4.4/32 (Metric: 10) AR4.4e-00 51 0x00000013 0xf304 682 0/0/0 Extended Reachability: 0000.0000.4444.00 (Metric: 0) Extended Reachability: 0000.0000.3333.00 (Metric: 0) 5 LSPs ``` AR4 database: ``` AR4# show isis database detail Area AA: IS-IS Level-1 link-state database: LSP ID PduLen SeqNumber Chksum Holdtime ATT/P/OL AR4.00-00 * 104 0x00000019 0xf562 507 1/0/0 Protocols Supported: IPv4 Area Address: 49.0003 Area Address: 49.0001 Hostname: AR4 TE Router ID: 4.4.4.4 Router Capability: 4.4.4.4 , D:0, S:0 Extended Reachability: 0000.0000.4444.50 (Metric: 10) IPv4 Interface Address: 4.4.4.4 Extended IP Reachability: 34.1.1.0/24 (Metric: 10) Extended IP Reachability: 45.1.1.0/24 (Metric: 10) Extended IP Reachability: 4.4.4.4/32 (Metric: 10) AR4.50-00 * 51 0x00000013 0x2188 462 1/0/0 Extended Reachability: 0000.0000.4444.00 (Metric: 0) Extended Reachability: 0000.0000.5555.00 (Metric: 0) AR5.00-00 92 0x00000017 0xaa26 457 0/0/0 Protocols Supported: IPv4 Area Address: 49.0003 Hostname: AR5 TE Router ID: 5.5.5.5 Router Capability: 5.5.5.5 , D:0, S:0 Extended Reachability: 0000.0000.4444.50 (Metric: 10) IPv4 Interface Address: 5.5.5.5 Extended IP Reachability: 45.1.1.0/24 (Metric: 10) Extended IP Reachability: 5.5.5.5/32 (Metric: 10) 3 LSPs IS-IS Level-2 link-state database: LSP ID PduLen SeqNumber Chksum Holdtime ATT/P/OL AR2.00-00 104 0x0000001e 0x38de 330 0/0/0 Protocols Supported: IPv4 Area Address: 49.0002 Area Address: 49.0001 Hostname: AR2 TE Router ID: 2.2.2.2 Router Capability: 2.2.2.2 , D:0, S:0 Extended Reachability: 0000.0000.3333.4a (Metric: 10) IPv4 Interface Address: 2.2.2.2 Extended IP Reachability: 12.1.1.0/24 (Metric: 10) Extended IP Reachability: 23.1.1.0/24 (Metric: 10) Extended IP Reachability: 2.2.2.2/32 (Metric: 10) AR3.00-00 111 0x0000001a 0xcc6b 420 0/0/0 Protocols Supported: IPv4 Area Address: 49.0001 Hostname: AR3 TE Router ID: 3.3.3.3 Router Capability: 3.3.3.3 , D:0, S:0 Extended Reachability: 0000.0000.3333.4a (Metric: 10) Extended Reachability: 0000.0000.4444.4e (Metric: 10) IPv4 Interface Address: 3.3.3.3 Extended IP Reachability: 23.1.1.0/24 (Metric: 10) Extended IP Reachability: 34.1.1.0/24 (Metric: 10) Extended IP Reachability: 3.3.3.3/32 (Metric: 10) AR3.4a-00 51 0x00000013 0x76eb 466 0/0/0 Extended Reachability: 0000.0000.3333.00 (Metric: 0) Extended Reachability: 0000.0000.2222.00 (Metric: 0) AR4.00-00 * 104 0x00000019 0x9bc6 471 0/0/0 Protocols Supported: IPv4 Area Address: 49.0003 Area Address: 49.0001 Hostname: AR4 TE Router ID: 4.4.4.4 Router Capability: 4.4.4.4 , D:0, S:0 Extended Reachability: 0000.0000.4444.4e (Metric: 10) IPv4 Interface Address: 4.4.4.4 Extended IP Reachability: 34.1.1.0/24 (Metric: 10) Extended IP Reachability: 45.1.1.0/24 (Metric: 10) Extended IP Reachability: 4.4.4.4/32 (Metric: 10) AR4.4e-00 * 51 0x00000013 0xf304 492 0/0/0 Extended Reachability: 0000.0000.4444.00 (Metric: 0) Extended Reachability: 0000.0000.3333.00 (Metric: 0) 5 LSPs ``` AR5 database: ``` AR5# show isis database detail Area AA: IS-IS Level-1 link-state database: LSP ID PduLen SeqNumber Chksum Holdtime ATT/P/OL AR4.00-00 104 0x00000019 0xf562 663 1/0/0 Protocols Supported: IPv4 Area Address: 49.0003 Area Address: 49.0001 Hostname: AR4 TE Router ID: 4.4.4.4 Router Capability: 4.4.4.4 , D:0, S:0 Extended Reachability: 0000.0000.4444.50 (Metric: 10) IPv4 Interface Address: 4.4.4.4 Extended IP Reachability: 34.1.1.0/24 (Metric: 10) Extended IP Reachability: 45.1.1.0/24 (Metric: 10) Extended IP Reachability: 4.4.4.4/32 (Metric: 10) AR4.50-00 51 0x00000013 0x2188 618 1/0/0 Extended Reachability: 0000.0000.4444.00 (Metric: 0) Extended Reachability: 0000.0000.5555.00 (Metric: 0) AR5.00-00 * 92 0x00000017 0xaa26 613 0/0/0 Protocols Supported: IPv4 Area Address: 49.0003 Hostname: AR5 TE Router ID: 5.5.5.5 Router Capability: 5.5.5.5 , D:0, S:0 Extended Reachability: 0000.0000.4444.50 (Metric: 10) IPv4 Interface Address: 5.5.5.5 Extended IP Reachability: 45.1.1.0/24 (Metric: 10) Extended IP Reachability: 5.5.5.5/32 (Metric: 10) 3 LSPs ``` Problem: 1. As we can see, AR2 receives the loopback address 1.1.1.1/32 from AR1 in the L1 LSP, but does not add the route to the L2 database, so AR3 does not receive the route. Similarly, AR3 has not learned the route 5.5.5.5/32 of AR5. 2. It turns out that AR1 can ping AR2, AR3 and AR4, but can't connect AR5, and AR3 can't connect AR1 and AR5. 3. If a new L1 device is added to the left of AR1, it will not be able to connect the three devices of AR3-AR5.

I’ll create a task in our vyos.dev to document it , if you can make a comment confirming it on FRR 9 , it would be great .