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Re: IP Routing problem after enabling MPLS?

  • From: Garry Glendown <garry@regio.net>
  • Date: Sat, 18 Sep 2004 21:20:25 +0200
  • CC: garry@regio.net, mpls-ops@mplsrc.com
  • Resent-Date: Sat, 18 Sep 2004 15:46:14 -0400
  • User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.0; en-US; rv:1.7.1) Gecko/20040707

sthaug@nethelp.no wrote:

> There are many Cisco FE interfaces that do not support higher MTUs than
> 1500, for instance PAs for 7200. This should not be a problem as long as
> you only use these on the customer facing side (towards the CE router).
> 
> On network facing side of your P or PE routers (towards other P and PE
> routers), you *need* at least 8 byte extra for 2 labels. You can either

That's how I understood it, too ..

> use a lower IP MTU in your network (ensuring there is room for at least
> two labels, preferably a bit more), or you can use interface types that

How does this help me with the packet transfer? Where would I set it 
lower in order to fix the problem? Setting it on both sides of the 
ethernet bridge didn't help me any (set "ip mtu" to 1488) ... should I 
instead set the MTU to 1488 on our uplink/peering interfaces?

> support a higher MTU than 1500. Most serial and SONET/SDH interfaces
> support considerably larger MTUs.

POS or E3 or so don't help me any on the Ethernet Bridge ... got the 
line instead of the E3 in order to try to save money on the equipment 
and handling (lines cost about the same per month) ...

So, why does the 7200 FE's say "max mtu 1580" ??

border-gw.ffm1#show contr fa0/1
Interface FastEthernet0/1 (idb 0x6274EBD8)
[..]
   rx cache size=400, rx cache end=272, rx_nobuffer=0
   max_mtu=1580

Tnx, -gg

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