• ISIS adjacencies is not forming on switch1 irb.102 interface.

• Switch 1 isis adjacency stuck in Initializing state.

Switch1> show isis adjacency

Interface System L State Hold (secs) SNPA

irb.101 switch2 3 Up 26

irb.102 switch2 3 Initializing 20 <<<<<<<<<<<

• Switch 2 isis adjacency not shown on irb.102.

Switch2> show isis adjacency

Interface System L State Hold (secs) SNPA

irb.101 switch1 3 Up 20
 

• All the configuration and mtu is ok.
• Switch1 sending the isis packets to Switch2, but switch2 not receiving the packets. 
• Below is the switch1 packet capture snippet

-----original packet-----

7c:e2:ca:5b:2c:xx > 09:00:2b:00:00:xx, ethertype 802.1Q (0x8100), length 110: vlan 102, p 0, LLC, dsap OSI (0xfe) Individual, ssap OSI (0xfe) Command, ctrl 0x03: OSI NLPID IS-IS (0x83): length 89

  Point-to-point Adjacency State TLV #240, length: 5

   Adjacency State: Down (2)

   Neighbor Extended Local circuit-ID: 0xd1bf5007

   0x0000: 0200 0002 3b

  Protocols supported TLV #129, length: 2

   NLPID(s): IPv4 (0xcc), IPv6 (0x8e)

   0x0000: cc8e

  IPv4 Interface address(es) TLV #132, length: 4

   IPv4 interface address: 209.191.80.7

   0x0000: d1bf 5007

   Area address (length: 7): 49.00xx.0310.2510

   0x0000: 0749 0001 0310 2510

  Restart Signaling TLV #211, length: 3

44:aa:50:f9:cc:xx > 09:00:2b:00:00:xx, ethertype 802.1Q (0x8100), length 1486: vlan 102, p 6, LLC, dsap OSI (0xfe) Individual, ssap OSI (0xfe) Command, ctrl 0x03: OSI NLPID IS-IS (0x83): length 1465

p2p IIH, hlen: 20, v: 1, pdu-v: 1, sys-id-len: 6 (0), max-area: 3 (0)

0x0000: 8314 0100 1101 0000

 source-id: 2001.5216.6126, holding time: 27s, Flags: [Level 1, Level 2]

 circuit-id: 0x01, PDU length: 1492

 0x0000: 0320 0152 1661 2600 1b05 d401

  Point-to-point Adjacency State TLV #240, length: 15

   Adjacency State: Initializing (1)

   Extended Local circuit-ID: 0x00000226

   Neighbor System-ID: 2001.5216.6127

   Neighbor Extended Local circuit-ID: 0x0000023b

   0x0000: 0100 0002 2620 0152 1661 2700 0002 3b

  Protocols supported TLV #129, length: 2

   NLPID(s): IPv4 (0xcc), IPv6 (0x8e)

   0x0000: cc8e

  IPv4 Interface address(es) TLV #132, length: 4

   IPv4 interface address: 209.191.80.6

   0x0000: d1bf 5006

  IPv6 Interface address(es) TLV #232, length: 16

   IPv6 interface address: fe80::46aa:5000:66f9:cc78

Jun 27 02:47:09.529894 ISIS L3 periodic xmit to 09:00:2b:xx:xx:05 interface irb.102 >>>>> send to switch2

Jun 27 02:47:15.107077 ISIS L3 hello from switch2 interface irb.102 absorbed. <<<<< received on switch1

• Below is the switch2 packet capture snippet.

Jun 27 02:45:26.606653 ISIS L3 periodic xmit to 09:00:2b:00:00:05 interface irb.102 >>>>>>>>>>>> only xmit no absorbed

7c:e2:ca:5b:2c:xx > 09:00:2b:00:00:xx, ethertype 802.1Q (0x8100), length 110: vlan 102, p 6, LLC, dsap OSI (0xfe) Individual, ssap OSI (0xfe) Command, ctrl 0x03: OSI NLPID IS-IS (0x83): length 89

p2p IIH, hlen: 20, v: 1, pdu-v: 1, sys-id-len: 6 (0), max-area: 3 (0)

0x0000: 8314 0100 1101 0000

 source-id: 2001.5216.6127, holding time: 27s, Flags: [Level 1, Level 2]

  Point-to-point Adjacency State TLV #240, length: 5

   Adjacency State: Down (2)

   Neighbor Extended Local circuit-ID: 0xd1bf5007

   0x0000: 0200 0002 3b

  Protocols supported TLV #129, length: 2

   NLPID(s): IPv4 (0xcc), IPv6 (0x8e)

   0x0000: cc8e

  IPv4 Interface address(es) TLV #132, length: 4

   IPv4 interface address: 209.191.80.7

   0x0000: d1bf 5007

  IPv6 Interface address(es) TLV #232, length: 16

   Area address (length: 7): 49.0001.0310.2510

   0x0000: 0749 0001 0310 2510

• When we Move x-link2 to ae0, isis on the irb.102 is up.
• based on the firewall filter configuration switch2 ae1 interface is receiving IS-IS packets [tested using isis all is mac address:09-00-2B-0O-00-05]
• No drops seen on ingress pipeline of PFE2 where the ae1's only child member et-0/0/35 is located.
• No drops at HALP layer.
• At CPUq ISIS packet is being received for PFE1 [where ae0's only child member et-0/0/23] is present whereas for PFE2 no packets received.
• So from PFE2 to RE the isis traffic is not flowing.

• Bounce the IRB interface.
• If the issue persist reconfigure the IRB interface.
• If issue not resolved reboot the switch.