[j-nsp] MX960 JunOS recommendations

[Krzysztof Szarkowicz]

Let me guess.

Your network is multivendor network (JNPR and CSCO) and some transit devices are CSCO?

CSCO and JNPR uses different algorithm to calculate default MPLS MTU (if MPLS MTU is not explicitely
configured) which results in 4 byte difference between CSCO side and JNPR side of the same link for
MPLS MTU (the IP MTU is equal on both ends, so no problem with OSPF).

If on JNPR side your MPLS MTU is say 1500 and on the CSCO side the MPLS MTU is 1504, when the CSCO
device send an BGP update packet towards JNPR device with size 1502, this packet is dropped by JNPR
device (as it is to big), and TCP ACK is not sent back. CSCO is keeping by resending this 1502 long
packet, and JNPR is constantly dropping. Thus, after hold timer expires, the Notification message is
sent.

I assume that with 9.3.R3.8 you didn't catched the '1502' packet sizes.

Could you check with some show commands, what is the MPLS MTU on both ends of the link (which is
terminated on CSCO on one side and JNPR on other side)?

//Krzysztof

-----Original Message-----
From: Tima Maryin [mailto:tima at transtelecom.net] 
Sent: Wednesday, 11 November, 2009 9:57
To: kszarkowicz at gmail.com
Cc: juniper-nsp at puck.nether.net
Subject: Re: [j-nsp] MX960 JunOS recommendations

What did you mean by "inappropriately configured" ?

There are the same mtu settings everywhere and traffic passes quite well.
And ospf session goes up without problems.

And how comes that "inappropriately configured IP and MPLS MTU" work well on 
9.3R3.8 ?


Krzysztof Szarkowicz wrote:
> It is not a nasty bug, but problem of inappropriately configured IP and MPLS MTUs on transit
nodes.
> 
> //Krzysztof
> 
> -----Original Message-----
> From: juniper-nsp-bounces at puck.nether.net [mailto:juniper-nsp-bounces at puck.nether.net] On Behalf
Of
> Tima Maryin
> Sent: Wednesday, 11 November, 2009 8:28
> To: juniper-nsp at puck.nether.net
> Subject: Re: [j-nsp] MX960 JunOS recommendations
> 
> 9.3R4.4 has a nasty bug which occures in setup when you have bgp session over 
> chain of few routers/links with ospf/ldp
> 
> bgp session occasionally goes down with notification timeout. Even when there is 
> no traffic at all and no physical errors
> 
> rollback to 9.3r3 helps though
> 
> 
> JTAC still not confirmed it, but it easlily can be reprodused in lab
> 
> 
> 
> Phil Shafer wrote:
>> Derick Winkworth writes:
>>> 9.3r4 indeed. Perhaps even 9.4r4 when that comes out.
>> FWIW: 9.5 has a number of scripting-related features, including
>> interactivity and remote RPC access.  We've been working to ensure
>> that scripting PRs are backported to at least 9.5.
>>
>> Thanks,
>>  Phil
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