Dumb device can't talk over MULTILINK PPP WAN link

Unanswered Question

I've got several remote locations with Verifone credit card machines (network based, not serial). When my links are setup like this, the machines work fine:

interface GigabitEthernet0/0.1

encapsulation dot1Q 123

ip address 10.1.xx.xx 255.255.255.0

ip helper-address 10.1.xx.xx

!

interface GigabitEthernet0/0.2

encapsulation dot1Q 223

ip address 10.2.xx.xx 255.255.255.0

ip access-group 121 in

ip helper-address 10.1.xx.xx

!

interface GigabitEthernet0/0.3

encapsulation dot1Q 323

ip address 10.3.xx.xx 255.255.255.0

ip pim sparse-mode

!

interface GigabitEthernet0/0.4

encapsulation dot1Q 423

ip address 10.4.xx.xx 255.255.255.0

ip access-group 120 in

!

interface GigabitEthernet0/1

ip address dhcp

shutdown

duplex auto

speed auto

media-type rj45

!

interface Serial0/1/0

ip unnumbered GigabitEthernet0/0.1

ip pim sparse-mode

service-policy output Serial-Policy

load-interval 30

!

interface Serial0/2/0

ip unnumbered GigabitEthernet0/0.1

ip pim sparse-mode

service-policy output Serial-Policy

load-interval 30

Everyone I've talked to says I should be using multilink PPP, but when I do, the credit card machine can't connect out through the WAN. Every other device works fine, PC's, IP Phones, etc. Just not the credit card machine. Here is the config with PPP:

interface Multilink 1

ip unnumbered GigabitEthernet0/0.1

ip pim sparse-mode

service-policy output Serial-Policy

ppp multilink

ppp multilink group 1

interface GigabitEthernet0/0.1

encapsulation dot1Q 123

ip address 10.1.xx.xx 255.255.255.0

ip helper-address 10.1.xx.xx

!

interface GigabitEthernet0/0.2

encapsulation dot1Q 223

ip address 10.2.xx.xx 255.255.255.0

ip access-group 121 in

ip helper-address 10.1.xx.xx

!

interface GigabitEthernet0/0.3

encapsulation dot1Q 323

ip address 10.3.xx.xx 255.255.255.0

ip pim sparse-mode

!

interface GigabitEthernet0/0.4

encapsulation dot1Q 423

ip address 10.4.xx.xx 255.255.255.0

ip access-group 120 in

!

interface GigabitEthernet0/1

ip address dhcp

shutdown

duplex auto

speed auto

media-type rj45

!

interface Serial0/1/0

no ip address

encapsulation ppp

ppp multilink

ppp multilink group 1

!

interface Serial0/2/0

no ip address

encapsulation ppp

ppp multilink

ppp multilink group 1

Again, every other device works fine, just not the credit card machine. I had to switch the config back and the CC machine started working again. I control both sides of the WAN link. I've tried "ppp multilink fragment disable" and that didn't help. Should I be using a loopback interface for the common IP address? Any ideas or suggestions?

I have this problem too.
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sundar.palaniappan Tue, 04/03/2007 - 07:00

If enabling multilink breaks connectivity for one application it sounds like a possible MTU issue. Try lowering the MTU to 1450 on the interface or use 'ip tcp adjust-mss 1450' if it's a TCP application and see if that helps.

HTH

Sundar

sundar.palaniappan Tue, 04/03/2007 - 12:34

You may have to run some debugs to see why the traffic fails. You may be able to find something with debug ppp multilink data or events. As with any debugs, exercise caution and run the debugs during during a maintenance window.

HTH

Sundar

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