On Tue, 30 Oct 2001 jlewis@lewis.org wrote:
> On Tue, 30 Oct 2001, Stephen Sprunk wrote:
>
> > > Also, i found in "sh ip bgp neighbor" output the following line:
> > "Datagrams
> > > (max data segment is 536 bytes)".
> >
> > Okay, TCP has for some reason negotiated a MSS of 536, which means a maximum
> > datagram size of 576, assuming you're using IPv4 and there are no IP or TCP
> > options present.
>
> Other than a small MTU somewhere on or between the routers, why might they
> do this? I just checked on a few routers (7513, 7206, 3640) running both
> iBGP and eBGP with peers at the other ends of point to point T3's,
> T1's or across our WAN. All of them show:
>
> Datagrams (max data segment is 536 bytes):
cisco's BGP implementation currently has one of two static maximum update
sizes, 256 or 512 bytes. Static means it ignores TCP MSS. If you depend
on this not changing you will get into trouble.
-Scott
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