Symptom
When the MTU of the dialer interface is configured with any value higher than 1492 with PPPoE already established, the MTU will reset to 1492 bytes. The router configuration will also show the MTU of 1492.
controller SHDSL 0
mode efm
dsl-group auto
interface Ethernet0
description ORCH=RESEAU
mtu 1580
pppoe-client dial-pool-number 1
pppoe-client ppp-max-payload 1572
!
interface dialer 1
ip address negotiated
mtu 1572
encapsulation ppp
ppp pap sent-username cisco password cisco
dialer pool 1
!
With the above configuration, the PPPoE session is getting established properly and the dialer interface is negotiated with the configured MTU 1572.
C888-1#sh int d1 | in MTU
MTU 1572 bytes, BW 56 Kbit/sec, DLY 20000 usec,
MTU 1572 bytes, BW 56 Kbit/sec, DLY 20000 usec,
However when we make any changes in the dialer MTU, it is getting reset to 1492
C888EA-1(config)#interface Dialer1
C888EA-1(config-if)#mtu 1564
C888EA-1#show interface Dialer1 | inc MTU
MTU 1492 bytes, BW 56 Kbit/sec, DLY 20000 usec,
MTU 1492 bytes, BW 56 Kbit/sec, DLY 20000 usec,
C888EA-1#show run interface Dialer1 | in mtu
mtu 1492
Conditions
PPPoE session should already been established .
Workaround
Shutdown the Dialer interface and then change the MTU. With the PPPoE session getting re-established the dialer interface will be assigned with the correct MTU.
Further Problem Description
This defect is specific for IOS-XE platforms. For IOS based platforms running on M&T trains, please refer to CSCwh73329.
