Hello,
I have a FC4 router that routes packets between two Ethernet networks using quagga 98.5 for ripd.
network 1 is a 172.27.1.0/24 and the other is 172.27.2.0/24. If I do a
ifconfig I get the following output.
eth0 Link encap:Ethernet HWaddr 00:04:23:AAE:E6
inet addr:172.27.1.31 Bcast:172.27.1.255 Mask:255.255.255.0
inet6 addr: fe80::204:23ff:feaa:dee6/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:443482 errors:0 dropped:0 overruns:0 frame:0
TX packets:382153 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:128107305 (122.1 MiB) TX bytes:110925374 (105.7 MiB)
Base address:0x8000 Memory:fae80000-faea0000

eth2 Link encap:Ethernet HWaddr 00:04:23:AB:30:90
inet addr:172.27.2.31 Bcast:172.27.2.255 Mask:255.255.255.0
inet6 addr: fe80::204:23ff:feab:3090/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:8649 errors:0 dropped:0 overruns:0 frame:0
TX packets:10092 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:805678 (786.7 KiB) TX bytes:5423479 (5.1 MiB)
Base address:0x8800 Memory:fafc0000-fafe0000

lo Link encap:Local Loopback
inet addr:127.0.0.1 Mask:255.0.0.0
inet6 addr: ::1/128 Scope:Host
UP LOOPBACK RUNNING MTU:16436 Metric:1
RX packets:565 errors:0 dropped:0 overruns:0 frame:0
TX packets:565 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:30556 (29.8 KiB) TX bytes:30556 (29.8 KiB)

Now every thing looks good and I can ping hosts from each network. The
problem is that network packets traveling across this router get fragmented
to 1492 MTU. This fragmentation is causing problems with printing, windows
networking, and general sluggish performace of the router. I know of the
fragmentation because If I traceroute from my AIX box I get the following
output.
# traceroute 172.27.1.31
trying to get source for 172.27.1.31
source should be 172.27.1.2
traceroute to 172.27.1.31 (172.27.1.31) from 172.27.1.2 (172.27.1.2), 30
hops max
outgoing MTU = 1500
1 csqrouter (172.27.1.31) 1 ms 0 ms 0 ms

#traceroute 172.27.2.31
trying to get source for 172.27.2.31
source should be 172.27.1.2
traceroute to 172.27.2.31 (172.27.2.31) from 172.27.1.2 (172.27.1.2), 30
hops max
outgoing MTU = 1500
1 csq6611.pa-ucl.com (172.27.1.30) 3 ms 2 ms 2 ms
2 csq6611.pa-ucl.com (172.27.1.30) 5 ms
fragmentation required, trying new MTU = 1492
2 172.27.2.31 (172.27.2.31) 4 ms 4 ms 4 ms

Why can't I stay with the 1500 MTU when forwarding the packets??? I have CISCO and Old IBM routers tha seem to have no problems forwarding 1500 byte packets.....

Thank you for your time...
Shane

some of the dsl lines used to have a problem with 1500 byte mtu .. so may be fc made it 1492.

nic should have no reason to do that ..you can try by doing
ifconfig with the right mtu size and see what happens

ifconfig eth? mtu xx should do it .. check the manpage