[c-nsp] BGP "keep alives throttled do to tcp", MTU mismatch?

[Scott Granados]

That makes sense.  I also noticed this really starting when the CPU is 
heavily nailed.  (looking at the time this started against some graphs).

Sounds reasonable I can try to bring the link up with the loop unloaded to 
see if that helps but I still sort of feel possible MTU issues but can't put 
my finger on it.  Some more googling shows that there can be issues if 
path-mtu-discovery and timestamps are enabled at the same time but I don't 
have a tcp timestamps entry in the global config.


-----Original Message----- 
From: David Prall
Sent: Thursday, July 21, 2011 4:28 PM
To: Scott Granados ; cisco-nsp at puck.nether.net
Subject: RE: [c-nsp] BGP "keep alives throttled do to tcp", MTU mismatch?

BGP Hellos are not sent with pak-priority, while they are marked IP 
Precedence 6. Thus they need to be prioritized if you have a congested link. 
That GE Port on the NPE-400 is subrate to begin with, so you could be 
dropping them before they even make it out or can be processed inbound.

David

--
http://dcp.dcptech.com


> -----Original Message-----
> From: cisco-nsp-bounces at puck.nether.net [mailto:cisco-nsp-
> bounces at puck.nether.net] On Behalf Of Scott Granados
> Sent: Thursday, July 21, 2011 4:01 PM
> To: cisco-nsp at puck.nether.net
> Subject: [c-nsp] BGP "keep alives throttled do to tcp", MTU mismatch?
>
> Hi, I have a puzzler.
>
> I have two Cisco 7206VXr routers one with a G1 and the other with a 400
> processor.
> Between them terminated on a gig interface on each side is an ILEC
> provided metro E connection that’s pretty vanilla using VLANs to
> address different connections.
>
> I have a /30 set up on a common VLAN between the two with the BGP peer
> set up on that /30.
>     After 3 minutes, my session will reset I’m assuming do to lack of
> keepalives / problems with MTU.  Lots of googling as pointed me at
> various MTU mismatch situations but I’m not sure what I’m doing wrong
> possibly assuming something is set “in an interesting way” between the
> sites on the ILEC network.
>
> On each interface I have the following
>
> int gig x/x
> mtu 1522
>
> Assuming 1500 for standard Ethernet and 22 for the VLAN tags.
> I also have the following set in global mode
> ip tcp path-mtu-discovery
>
> On both VXR devices code 12.4-25C is being run.
>
>     I would appreciate any pointers to investigate.  What have I
> missed?
>
>
> Thanks
> Scott
>
>
>
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