From: Messina, John V (john@crimsoncti.com)
Date: Sun Nov 09 2003 - 00:54:58 GMT-3
We have a situation with an ISP that's a little strange. We are
multihomed with 2 T1's to 2 ISP's for a long time. We are trying to add
a third ISP via an Ethernet handoff and are running into fragmentation
issues. The layout for the new ISP is this
MYFirewall>>my3550>dot1Q>isp3550>>ISPfiberRing>>ISP3550>ISP2948>>ISP1200
0>>internet
So whenever we plug the firewall into the 3550 and eliminate the other 2
ISP's from the equation and use only this Ethernet ISP most users and
servers cannot browse the internet
And traffic inbound does not work. You can telnet to my web servers on
port 80 but you cannot view it in IE. Similarly you can telnet to the MS
terminal servers on 3389 but cannot connect via an RDP client.
We have gone outside the firewall to eliminate it as a source. We have
plugged in a 3640 to do all routing instead of the 3550 and enabled path
mtu discovery since the 3550 does not support it ( if it does let me
know) We have enableb jumbo packet support with the sys mtu 1546
command on the 3550. We are using a dot1Q trunk between our 3550 and the
ISP for the purposes of video conferencing on their ring. We have
clients on the ring so this ISP just allows certain vlans over certain
trunks. To me at least this points to an MTU issue along the way
somewhere because fragmentation is definitely occurring.
We have asked the ISP to enable jumbo packet support on the switches in
the path but they have not done this yet. We have tried all different
combinations of MTU changes on servers and pmtud disabling.
I am curious if anyone has any theories on how to resolve this.
Thanks for any suggestions
This archive was generated by hypermail 2.1.4 : Fri Dec 12 2003 - 12:29:09 GMT-3