dropping connections over private T1 with cisco 1751′s at each end

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Cisco
I keep dropping connection over a private t1 spanned between two 1751 routers. This is most apparent when I am trying to open large files (especially Access) that are greater than 3mb. One of the routers is configured to also act as a dhcp server. the following are the configurations: STATEST#show startup-config Using 1844 out of 29688 bytes ! version 12.2 no parser cache service timestamps debug uptime service timestamps log uptime service password-encryption ! hostname STATEST ! enable secret 5 ******** enable password ******** ! memory-size iomem 25 ip subnet-zero ! ! no ip dhcp conflict logging ip dhcp excluded-address 192.168.10.241 192.168.10.255 ip dhcp excluded-address 192.168.10.1 192.168.10.50 ! ip dhcp pool 192.168.10.0/24 network 192.168.10.0 255.255.255.0 default-router 192.168.10.4 dns-server 192.168.1.254 204.17.65.2 ! ! ip multicast-routing ip cef ip ssh time-out 120 ip ssh authentication-retries 3 ! crypto mib ipsec flowmib history tunnel size 200 crypto mib ipsec flowmib history failure size 200 ! ! ! interface FastEthernet0/0 ip address 192.168.10.4 255.255.255.0 ip helper-address 192.168.1.254 ip pim dense-mode speed auto half-duplex ! interface Serial0/0 ip address 192.168.5.2 255.255.255.252 ip pim dense-mode ip igmp join-group 224.0.1.0 ip igmp unidirectional-link no fair-queue serial restart_delay 2 service-module t1 framing sf service-module t1 linecode ami service-module t1 timeslots all speed 56 ! ip default-gateway 192.168.5.1 ip classless no ip forward-protocol udp ip route 0.0.0.0 0.0.0.0 192.168.5.1 ip route 192.168.1.0 255.255.255.0 192.168.5.1 no ip http server ip pim bidir-enable ! ! banner motd ^CWelcome to the State Street router. Unauthorized access is prohibited!^C ! line con 0 password 7 ******* login line aux 0 line vty 0 4 password 7 ******* login ! end ============================================= GEP#show startup-config Using 1202 out of 29688 bytes ! version 12.2 no parser cache service timestamps debug uptime service timestamps log uptime service password-encryption ! hostname GEP ! enable secret 5 ******* enable password 7 ******* ! memory-size iomem 25 ip subnet-zero ! ! ! ip multicast-routing ip ssh time-out 120 ip ssh authentication-retries 3 ! crypto mib ipsec flowmib history tunnel size 200 crypto mib ipsec flowmib history failure size 200 ! ! ! interface FastEthernet0/0 ip address 192.168.1.4 255.255.255.0 ip pim dense-mode speed auto half-duplex ! interface Serial0/0 ip address 192.168.5.1 255.255.255.252 ip pim dense-mode ip igmp join-group 224.0.1.0 ip igmp unidirectional-link serial restart_delay 2 service-module t1 framing sf service-module t1 linecode ami service-module t1 timeslots all speed 56 ! ip default-gateway 192.168.1.1 ip classless ip route 0.0.0.0 0.0.0.0 192.168.1.1 ip route 192.168.10.0 255.255.255.0 192.168.5.2 no ip http server ip pim bidir-enable ! ! banner motd ^CWelcome to the GEP router. Unauthorized access is prohibited!^C ! line con 0 password 7 ******* login line aux 0 line vty 0 4 password 7 ******* login ! no scheduler allocate end
ASKED: January 22, 2006  12:28 PM
UPDATED: January 25, 2006  12:59 PM

Answer Wiki

Thanks. We'll let you know when a new response is added.

The interesting things I see about the configuration is the half-duplex setting on the F0/1 interfaces (make sure you don’t have a duplex mismatch), neither side of your T1 is injecting timing, and are you certain it’s sf and not esf framing on the T1?

Check your packet size to ensure that they aren’t too large and require fragmentation. Also make sure that the Don’t Fragment bit is not set on either the client or server side. You may have to change your MTU size and mangle the packets to remove the DF bit if this is your problem.

Finally, have you checked your Serial interface counters for interface resets and carrier loss? You might have a problem with the circuit.

Hope this points you in the right direction.

SF

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  • Bobkberg
    Sonyfreek makes several good points. Autodetect of ethernet speed and duplex is fraught with problems. Something else I wondered about is whether these networks are routed or bridged? Have you looked at the relevant logs on each side of the connection to see if there's anything interesting? Bob
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