IS-IS and IPv6 LLA next-hop - just Arista, or everyone?

Mark Tinka mark at
Tue May 4 04:21:12 UTC 2021

On 5/4/21 03:28, Adam Thompson wrote:
> Hey, just checking as I don’t have any Cisco or Extreme or Juniper 
> gear running IS-IS to verify myself…
> On current Arista (7280SR2K) and older Brocade (MLXe) routers, the 
> IPv6 next-hop address in IS-IS seems to always be the link-local 
> address of the neighbour, instead of any manually-assigned address on 
> the interface. I believe this is **not** the case with Cisco, in 
> particular.  Not sure about other vendors, I don’t have any handy that 
> can run IS-IS.  I don’t appear to have any knobs to control this 
> behaviour, and haven’t found anything related in the docs.
> Can anyone confirm that Cisco or other vendors does/do not do this 
> (prefer LLA over GUA)?


2c0f:feb0::1/128   *[IS-IS/18] 02:43:49, metric 5870
                        to fe80::1205:caff:fe86:4ac3 via et-4/0/2.0
                        to fe80::5287:89ff:fef3:25c3 via et-4/0/2.0
                        to fe80::1205:caff:fe86:4b10 via et-5/0/2.0
                     >  to fe80::5287:89ff:fef3:2610 via et-5/0/2.0


I2  2C0F:FEB0::1/128 [115/6410]
      via FE80::1205:CAFF:FE86:4AC3, TenGigabitEthernet1/0/0
      via FE80::1205:CAFF:FE86:4B10, TenGigabitEthernet0/0/0
      via FE80::5287:89FF:FEF3:25C3, TenGigabitEthernet1/0/0
      via FE80::5287:89FF:FEF3:2610, TenGigabitEthernet0/0/0


i L2 2c0f:feb0::1/128
       [115/5870] via fe80::1205:caff:fe86:4b10, 02:45:22, 
HundredGigE0/3/0/0 (!)
       [115/5810] via fe80::f60f:1bff:feb0:75c4, 02:45:22, 

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