Symptom
In a segment-routing mpls setup using non-default SRGB range, after a router reload, ISIS may fail to allocate the SRGB range:
RP/0/RSP0/CPU0:Jan 19 22:52:42.549 IST: isis[1013]: %ROUTING-ISIS-4-SRGB_ALLOC_FAIL : ISIS (core): SRGB allocation failed: 'SRGB reservation not successful for [16000,275999], SRGB (16000 275999, SRGB_ALLOC_CONFIG_PENDING, 0x3) (So far 32 attempts). Make sure label range is free'
And all services depending on SR and SRGB will fail.
Issue is very timing sensitive and very difficult to hit.
Conditions
- can only be hit after a router reload
- segment-routing mpls setup using non-default SRGB range only:
router isis
address-family [ipv4 | ipv6] unicast
segment-routing mpls
segment-routing
global-block
Default SRGB range is: 16000 23999
Workaround
There's no workaround.
Because it’s very difficult to hit, a 2nd reload will recover the router most of the time.
Further Problem Description
Since router reload is always disruptive and router will almost always recover after a 2nd reload, the impact is not as big as it seems.
