[c-nsp] TCP Throughput / MTU problem ? with Cisco 7304 andMPLSVPN's

[Eric Kagan]

> > Jan  8 22:04:47 est: %MFI-3-MPLS_MTU_SET: Setting mpls mtu 
> to 1520 on
> > GigabitEthernet1 which is higher than the interface mtu 
> 1500.  This could
> > lead to packet forwarding problems including packet drops.
> 
> Sometimes the controllers allow larger packets to be sent, but there's
> no guarantee. Would there be any problems associated with adjusting
> interface MTU up everywhere? Any limits on the data link layer?

I wasn't sure if there would be any ill effect on non-MPLS traffic and since
I had not changed it on the 7206's I figured there was some other issue.
There are no limits, I will try that, thanks.  

> 
> > I have not seen any problems with ICMP.  I can ping between 
> the 2 P routers
> > connected on the fiber up to 2000 bytes without a problem:
> > 
> > #ping
> > Sending 5, 1480-byte ICMP Echos to 66.203.65.25, timeout is 
> 2 seconds:
> > !!!!!
> > Success rate is 100 percent (5/5), round-trip min/avg/max = 1/1/4 ms
> > 
> > Sending 5, 1500-byte ICMP Echos to 66.203.65.25, timeout is 
> 2 seconds:
> > !!!!!
> > Success rate is 100 percent (5/5), round-trip min/avg/max = 1/1/4 ms
> > 
> > Sending 5, 1520-byte ICMP Echos to 66.203.65.25, timeout is 
> 2 seconds:
> > !!!!!
> > Success rate is 100 percent (5/5), round-trip min/avg/max = 1/1/1 ms
> > 
> > Sending 5, 1546-byte ICMP Echos to 66.203.65.25, timeout is 
> 2 seconds:
> > !!!!!
> > Success rate is 100 percent (5/5), round-trip min/avg/max = 1/1/4 ms
> > 
> > Sending 5, 2000-byte ICMP Echos to 66.203.65.25, timeout is 
> 2 seconds:
> > !!!!!
> > Success rate is 100 percent (5/5), round-trip min/avg/max = 1/1/4 ms
> 
> You have to set the DF bit, or else the routers will just fragment and
> reassemble. It's an extended ping option.

It allows 1500, not 1501 or larger.....

Eric