Secret BGP Timer?

[chrisbell1]

Hello there,

I'm trying to track down the timer which triggers the event to send a BGP update to a peer when configuration has changed for example a route-map configured on a neighbor.

When doing a debug on a router running BGP it appears that once this "Policy content change timer " timer expires a route refresh is kicked off to affected neighbors to push updated routing information.

This timer happens at a different schedule to that of the BGP scan timer. 

Nov 29 21:11:41.211: BGP: TX IPv4 Unicast Grp global 23 Policy content change timer expired.
*Nov 29 21:11:41.215: BGP: TX IPv4 Unicast Mem global 23 1 200.200.200.2 Full refresh requested.
*Nov 29 21:11:41.219: BGP: TX IPv4 Unicast Mem global 23 1 200.200.200.2 Refresh has to wait for net prepend.

Can anyone clarify what this timer is and its details? I can't find any information on it.

Cheers,

[Georg Pauwen]

Hello,

I cannot find anything on that specific log entry either, but I guess it must have something to do with BGP NSF (Nonstop Forwarding), do you have that configured by any chance ?

[chrisbell1]

Hi there,

No NSF configured. I might log a TAC case and ask for some info.

Will report back!

Cheers,

[GavinS]

---

@chrisbell1 wrote:

Hello there,

I'm trying to track down the timer which triggers the event to send a BGP update to a peer when configuration has changed for example a route-map configured on a neighbor.

When doing a debug on a router running BGP it appears that once this "Policy content change timer " timer expires a route refresh is kicked off to affected neighbors to push updated routing information.

This timer happens at a different schedule to that of the BGP scan timer. 

Nov 29 21:11:41.211: BGP: TX IPv4 Unicast Grp global 23 Policy content change timer expired.
*Nov 29 21:11:41.215: BGP: TX IPv4 Unicast Mem global 23 1 200.200.200.2 Full refresh requested.
*Nov 29 21:11:41.219: BGP: TX IPv4 Unicast Mem global 23 1 200.200.200.2 Refresh has to wait for net prepend.

Can anyone clarify what this timer is and its details? I can't find any information on it.

Cheers,

---

Hi, did you ever get to the bottom of this?

I've just found the same timer is the reason my route updates are taking 30 seconds to be advertised to my BGP peers after a route-map change.

Thanks,

Gavin

[georgiy_b]

duplicate

[georgiy_b]

So I have found this behavior too. It was kinda funny to read about all those soft and hard resets you need to do in order to implement policy change. And then you see it is being implemented automatically even with route refresh ( and/or any other negotiated capability) turned of.

As log messages suggest it has something to do with two things:

- Timer: I looked at all possibly relevant settings under "sh run all", nothing usefull there unfortunately.
- Group: in BGP debug you may see that 'group' is mentioned several times

BGP: TX IPv4 Unicast Tab Policy change timer expired.
BGP: TX IPv4 Unicast Mem global 10.7.2.2 Changing state from BLOCKED to WAIT (pending advertised bit allocation).
BGP: TX IPv4 Unicast Mem global 10.7.2.2 Match with group 5 failed (outbound routemap).
BGP: TX IPv4 Unicast Mem global 10.7.2.2 Match with group 7 failed (internal/external).
BGP: TX IPv4 Unicast Mem global 10.7.2.2 Match with group 8 failed (internal/external).
BGP: TX IPv4 Unicast Grp global 10 Created.
BGP: TX IPv4 Unicast Wkr global 10 Cur Blocked (not in list).
BGP: TX IPv4 Unicast Wkr global 10 Ref Blocked (not in list).
BGP: TX IPv4 Unicast Rpl global 10 1 Created.
BGP: TX IPv4 Unicast Rpl global 10 1 Pathext bitfield index 2 allocated.
BGP: TX IPv4 Unicast Mem global 10 1 10.7.2.2 Added to group (now has 1 members).
BGP: TX IPv4 Unicast Mem global 10 1 10.7.2.2 Staying in WAIT state (current walker waiting for net prepend).
BGP: TX IPv4 Unicast Top global Start pathext prepend.
BGP: TX IPv4 Unicast Tab Pathext prepend full table refresh.

Could it be BGP peer group? Well, I think it has nothing to do with that, unless peers are added to some peer group by default, which is unlikely. It leaves us with the only answer, I think:

It is dynamic update group's timer and log output we see. There is more information about this featute here.

a new algorithm was introduced that dynamically calculates and optimizes update groups of neighbors that share the same outbound policies and can share the same update messages. No configuration is required to enable the BGP dynamic update group and the algorithm runs automatically. When a change to outbound policy occurs, the router automatically recalculates update group memberships and applies the changes by triggering an outbound soft reset after a 1-minute timer expires.

Inbound policy changes are ignored and still require soft/hard reset.

BGP: TX IPv4 Unicast Mem global 10 1 3.3.3.3 Ignoring dummy policy change.
BGP: TX IPv4 Unicast Mem global 10 1 10.6.2.2 Ignoring dummy policy change.