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Problem with LFI fragment reassembly

 
 
Dieter Jansen
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Posts: n/a
 
      05-20-2005
Hi Folks,

I have been working with a couple of clients who have ADSL WANs
(over a private IP provider, not the public Internet) who are
experimenting with QoS and LFI.

The first client runs c837-k9o3sy6-mz.123-2.T.bin on a bunch of
837s, whilst the second runs c1700-k9o3sy7-mz.122-4.T7.bin on
1751s with ADSL WICs.

I was able to add QoS and LFI to the 837s without much drama but
I've had problems with the 1751s. When I add LFI to the 1751s
the central site cannot ping PCs on the remote LAN with packets
larger than 600 bytes. Interestingly it can ping the remote
router itself with large packets. Switching ppp multilink off
restores correct operation.

The 1751 does seem to get into multilink LFI mode as there is
the usual pause when I enable multilink and then a "sh int di1"
starts to show the virtual-access interfaces and "interleaves"
appear in the stats display.

I assume that 600 bytes corresponds to 10 msec of the 512 Kbps
bandwidth as I'm using "ppp multilink fragment delay 10".

The routers are not entirely identical as they have had quite
different histories, so I'm assuming that the problem 1751 has
a setting that is preventing fragment reassembly to the LAN
interface???

The clients are't keen on me posting full configs, but the
following may be enough to allow somone to spot the obvious
error

The (working) 837 router looks like:

version 12.3
...
ip cef
...
policy-map QoS-XXX
...
policy-map DiffServ-Marking-XXX
...
interface Ethernet0
ip address x.x.x.x 255.255.255.0
service-policy input DiffServ-Marking-XXX
ip route-cache flow
no ip mroute-cache
hold-queue 100 out
...
interface ATM0
no ip address
no ip mroute-cache
no atm ilmi-keepalive
pvc 8/35
encapsulation aal5snap
protocol ip inarp
protocol ppp dialer
dialer pool-member 1
!
dsl operating-mode auto
dsl power-cutback 0
bridge-group 1
hold-queue 224 in
!
interface ATM0.1 point-to-point
no ip mroute-cache
...
interface Dialer1
bandwidth 512
ip address negotiated
service-policy output QoS-XXX
encapsulation ppp
ip tcp header-compression
no ip mroute-cache
dialer pool 1
dialer idle-timeout 0
dialer persistent delay initial 30
dialer persistent delay 30
dialer persistent max-attempts 3
dialer-group 1
keepalive 10 3
ppp authentication chap callin
ppp chap hostname http://www.velocityreviews.com/forums/(E-Mail Removed)x
ppp chap password 7 xxxxxxxxxxxxxxxxx
ppp multilink
ppp multilink fragment delay 10
ppp multilink interleave
hold-queue 224 in

The (broken) 1751 router looks like:

version 12.2
...
ip cef
...
policy-map QoS-XXX
...
policy-map DiffServ-Marking-XXX
...
interface ATM0/0
no ip address
no ip mroute-cache
atm vc-per-vp 256
no atm ilmi-keepalive
pvc 8/35
encapsulation aal5snap
protocol ip inarp
protocol ppp dialer
dialer pool-member 1
!
dsl operating-mode auto
no fair-queue
bridge-group 1
hold-queue 224 in
!
interface ATM0/0.1 point-to-point
no ip mroute-cache
...
interface FastEthernet0/0
ip address x.x.x.x 255.255.255.0
service-policy input DiffServ-Marking-XXX
no ip mroute-cache
speed auto
hold-queue 100 out
...
interface Dialer1
bandwidth 512
ip address negotiated
service-policy output QoS-XXX
encapsulation ppp
ip tcp header-compression
no ip mroute-cache
dialer pool 1
dialer idle-timeout 0
dialer persistent delay initial 30
dialer persistent delay 30
dialer persistent max-attempts 3
dialer-group 1
ppp authentication chap callin
ppp chap hostname (E-Mail Removed)x
ppp chap password 7 xxxxxxxxxxxxxxxxxxxxxxx
ppp multilink
ppp multilink fragment delay 10
ppp multilink interleave

Can anyone spot what's wrong? I suppose it could be the
router model, the IOS version, or perhaps the ISP's core
router config that are at fault, but I think I'm doing
something that prevents reassembly.

Any thoughts greatly appreciated.

Cheers, Dieter.




 
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