From: marvin greenlee (marvin@ccbootcamp.com)
Date: Thu Feb 17 2005 - 17:25:33 GMT-3
The switch will not let you change the MTU for the VLAN to be LESS than the
system MTU. In the examples below, Cat1 has a system MTU of 1503, and Cat2
has a system MTU of 1500. When trying to change the MTU on the VLAN, the
Cat will not allow you to configure for a value higher than the system.
** Cat1 **
C4Cat1#show system mtu
System MTU size is 1503 bytes
C4Cat1#conf t
Enter configuration commands, one per line. End with CNTL/Z.
C4Cat1(config)#int vlan 113
C4Cat1(config-if)#ip mtu 1600
% Invalid IP MTU specified; minimum 68, maximum 1503
** Cat2 **
C4Cat2#show system mtu
System MTU size is 1500 bytes
C4Cat2#conf t
Enter configuration commands, one per line. End with CNTL/Z.
C4Cat2(config)#int vlan 113
C4Cat2(config-if)#ip mtu ?
<68-1000000> MTU (bytes)
C4Cat2(config-if)#ip mtu 1600
% Invalid IP MTU specified; minimum 68, maximum 1500
To answer your second question, changing a vlan's ip MTU does not require a
reload.
** Set Cat2's VLAN MTU to 1400 **
C4Cat2(config)#int vlan 113
C4Cat2(config-if)#ip mtu 1400
** Ping from Cat1, size 1440 with DF set **
C4Cat1#ping
Protocol [ip]:
1d01h: %SYS-5-CONFIG_I: Configured from console by console
Target IP address: 144.4.113.36
Repeat count [5]:
Datagram size [100]: 1440
Timeout in seconds [2]:
Extended commands [n]: y
Source address or interface: vlan 113
Type of service [0]:
Set DF bit in IP header? [no]: yes
Validate reply data? [no]:
Data pattern [0xABCD]:
Loose, Strict, Record, Timestamp, Verbose[none]:
Sweep range of sizes [n]:
Type escape sequence to abort.
Sending 5, 1440-byte ICMP Echos to 144.4.113.36, timeout is 2 seconds:
.....
Success rate is 0 percent (0/5)
** Change MTU on Cat 2 **
C4Cat2(config-if)#ip mtu 1450
** Ping again with DF set **
C4Cat1#ping
Protocol [ip]:
1d01h: %SYS-5-CONFIG_I: Configured from console by console
Target IP address: 144.4.113.36
Repeat count [5]:
Datagram size [100]: 1440
Timeout in seconds [2]:
Extended commands [n]: y
Source address or interface: vlan 113
Type of service [0]:
Set DF bit in IP header? [no]: yes
Validate reply data? [no]:
Data pattern [0xABCD]:
Loose, Strict, Record, Timestamp, Verbose[none]:
Sweep range of sizes [n]:
Type escape sequence to abort.
Sending 5, 1440-byte ICMP Echos to 144.4.113.36, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 1/2/4 ms
C4Cat1#
Marvin Greenlee, CCIE#12237, CCSI# 30483
Network Learning Inc
marvin@ccbootcamp.com
www.ccbootcamp.com (Cisco Training)
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
ccie2be
Sent: Wednesday, February 16, 2005 10:17 AM
To: Group Study
Subject: Changing system mtu vs vlan mtu [bcc][faked-from][bayes]
Importance: Low
Hi guys,
If the system mtu is left at it's default value of 1500, but a vlan's mtu
is
set to 1504 to support 801.1Q tunneling, will that work as well?
Or, does the system's mtu have to be changed to 1504?
Assume the access vlan on the Service Provider's switch which is used for
tunneling is the vlan whose mtu is changed.
Also, I know that for the system mtu change to take effect, the switch has
to
be reloaded. Is the same true when the vlan mtu is changed?
TIA, Tim
This archive was generated by hypermail 2.1.4 : Thu Mar 03 2005 - 08:51:22 GMT-3