[j-nsp] SRX 550 BGP Flapping

[Payam Chychi]

On Tue, Jan 30, 2018 at 9:29 AM Alexander Arseniev <arseniev at btinternet.com>
wrote:

> Hello,
>
> BGP KA size is 19 bytes without authentication, circa 39 with. Plus IP
> overhead, plus Ethernet OVH - still below 100 B.
>
> SRX reth default MTU is 1500B.
>
> Are You sure that checking & setting MTU helps to fix BGP holdtime expiry?
>
> I would bet that either SRX550 reth interface is saturated, or SRX550
> CPU is busy.
>
> HTH
>
> Thx
> Alex
>
>
> On 30/01/2018 06:25, Emille Blanc wrote:
> > You might want to check the MTU of the path, or ensure that pmtu is
> enabled.
> > It looks like you're using a redundant ethernet interface (reth). If
> you're using a non-standard MTU, make sure it is set correctly for its
> member interface(s).
> >
> > ________________________________________
> > From: juniper-nsp [juniper-nsp-bounces at puck.nether.net] On Behalf Of
> sameer mughal [pcs.sameer1 at gmail.com]
> > Sent: Monday, January 29, 2018 8:20 PM
> > To: juniper-nsp at puck.nether.net
> > Subject: Re: [j-nsp] SRX 550 BGP Flapping
> >
> > I have seen hold time error. what will be the fix on this issue?
> >
> >
>
> _______________________________________________
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>
 Bgp exchanges routes, those routes get sent as an update packet, that
packet can fill up the size of the packet to the mtu-ip/tcp(40byte), so
yes, if you have mix match of mtu, your bgp session will
drop/reconnect/drop... (repeat) if the update pkt size gets fragmented


-- 
Payam Tarverdyan Chychi
Network Security Specialist / Network Engineer