[c-nsp] BGP convergence with jumbo frames

[Pete Kruckenberg]

On Mon, 2 Aug 2004 lee.e.rian at census.gov wrote:

> > These links have to support
> > 9000-byte jumbo frames.
> 
> Even if the links allow 9000 byte Ethernet frames the IP
> packet length is still limited to 1500 bytes; you also
> need to adjust the IP max packet length.

Apparently the IP MTU is automatically adjusted with the 
interface MTU. A "show ip interface" says the MTU is 9000. 
Setting "ip mtu 9000" on the interface didn't change it.

> Just out of curiosity, if you do a "sh ip traffic" on
> one of these routers what do you get for the number of
> fragmented packets?

Sending router:
 IP statistics:
  Rcvd:  4112624 total, 1137829 local destination
         0 format errors, 0 checksum errors, 522 bad hop count
         0 unknown protocol, 0 not a gateway
         0 security failures, 0 bad options, 0 with options
  Opts:  0 end, 0 nop, 0 basic security, 0 loose source route
         0 timestamp, 0 extended security, 0 record route
         0 stream ID, 0 strict source route, 0 alert, 0 cipso
         0 other
  Frags: 0 reassembled, 0 timeouts, 0 couldn't reassemble
         0 fragmented, 0 couldn't fragment
  Bcast: 8527 received, 272 sent
  Mcast: 750967 received, 1237574 sent
  Sent:  1612034 generated, 490088 forwarded
  Drop:  2155 encapsulation failed, 0 unresolved, 0 no adjacency
         9 no route, 0 unicast RPF, 0 forced drop
  Drop:  0 packets with source IP address zero


Receiving router:
 IP statistics:
  Rcvd:  1058371 total, 795542 local destination
         0 format errors, 0 checksum errors, 71367 bad hop count
         0 unknown protocol, 0 not a gateway
         0 security failures, 0 bad options, 0 with options
  Opts:  0 end, 0 nop, 0 basic security, 0 loose source route
         0 timestamp, 0 extended security, 0 record route
         0 stream ID, 0 strict source route, 0 alert, 0 cipso
         0 other
  Frags: 0 reassembled, 0 timeouts, 0 couldn't reassemble
         0 fragmented, 0 couldn't fragment
  Bcast: 1755 received, 0 sent
  Mcast: 132659 received, 134222 sent
  Sent:  780542 generated, 65805 forwarded
  Drop:  4 encapsulation failed, 0 unresolved, 0 no adjacency
         0 no route, 0 unicast RPF, 0 forced drop
  Drop:  0 packets with source IP address zero