05-20-2008 07:53 AM - edited 03-05-2019 11:06 PM
Here is the root of my problem...I think. I have two vlans set up. Vlan1 and Vlan172. I can ping between them fine, unless the packet is 1501 bytes or larger. I am not setting the DF bit on any pings. I assume the packet should fragment if it is larger than the MTU. Instead I get a Destionation host unreachable if done from windows and timeouts if done from a router or switch. Where do i need to start looking? Here are the router VLAN code snippits.
interface FastEthernet0/1.1
bandwidth 10000000
encapsulation dot1Q 1 native
ip address 172.4.1.254 255.255.0.0
ip nbar protocol-discovery
ip pim dense-mode
ip virtual-reassembly
no snmp trap link-status
!
interface FastEthernet0/1.172
bandwidth 10000000
encapsulation dot1Q 172
ip address 172.31.251.250 255.255.255.0
ip pim dense-mode
no snmp trap link-status
And on the switch:
interface Vlan1
ip address 172.4.1.253 255.255.0.0
!
interface Vlan172
description VOICEVLAN
ip address 172.31.251.254 255.255.255.0
ip helper-address 172.31.251.254
ip helper-address 172.4.1.254
priority-group 1
And some assorted switchports:
interface FastEthernet0/21
switchport trunk encapsulation dot1q
service-policy input VOICE
srr-queue bandwidth share 10 10 60 20
srr-queue bandwidth shape 10 0 0 0
auto qos voip trust
storm-control broadcast level 1.00
random-detect
spanning-tree portfast
!
interface FastEthernet0/22
switchport trunk encapsulation dot1q
service-policy input VOICE
srr-queue bandwidth share 10 10 60 20
srr-queue bandwidth shape 10 0 0 0
auto qos voip trust
storm-control broadcast level 1.00
random-detect
spanning-tree portfast
!
interface FastEthernet0/23
switchport access vlan 172
switchport trunk encapsulation dot1q
switchport mode access
service-policy input VOICE
srr-queue bandwidth share 10 10 60 20
srr-queue bandwidth shape 10 0 0 0
auto qos voip trust
storm-control broadcast level 1.00
random-detect
spanning-tree portfast
Does anyone have any idea what may be the issue here. Basically what I am seeing, anytime windows (VLAN1) needs to send a packet larger than 1472 across the wan (the wan link is on VLAN172), the packet needs fragmented, but instead of doing that, it gets dropped/lost.
Thanks to all in advance.
Solved! Go to Solution.
05-20-2008 09:18 AM
Can you send packets larger that 1500 on the same Vlan ?
Can you post the entire config from the router ?
__
Edison.
05-20-2008 08:04 AM
John,
You could try enabling jumbo frames on the WAN:-
HTH.
05-20-2008 08:19 AM
I do not think that would help the local situation though, would it? I have devices plugged into the same switch that can't pass anything over 1500 bytes because they are on two different VLANS. All VLAN MTU's are at 1500.
Why will the packet not fragment is the root issue I think....
Thanks.
05-20-2008 09:18 AM
Can you send packets larger that 1500 on the same Vlan ?
Can you post the entire config from the router ?
__
Edison.
05-20-2008 09:27 AM
Yes. I can send virtually any size packet on the same VLAN. Cisco Tac has finally touched base with me. He is having me try something right now. It requires a reboot so I will not know for an hour or so. If that bombs off I will go ahead and post the entire config.
Thank you
05-21-2008 05:32 AM
Thanks everyone. The issue is solved. The Cisco tech was having problems too. He was sharp cookie though. We first tried the Jumbo frame thing on the switch. That did not help. Finally we had to go line by line through the router code. There were a couple of lines that neither one of us could explain why they were there. "ip nbar protocol-discovery" and "ip virtual-reassembly" was applied to the interface of VLAN1. We removed both but the tech said he is sure it was the ip virtual-reassembly command causing the issue.
Everything seems to be working fine so far. It is one of those issues where I hope we didn't break something while fixing something else.
Thanks for everyone's help.
Discover and save your favorite ideas. Come back to expert answers, step-by-step guides, recent topics, and more.
New here? Get started with these tips. How to use Community New member guide