What if there is a conflict between AUX port dialing and fast switching?

Fault symptom

The company's LAN uses the ddnleased line to access the Internet. It consists of A network connected by the CISCO 1751 router and B network connected by the CISCO 3662 router. When the ddnleased line is not used, I connect the CISCO 1751 router to the CISCO 3662NM-16AS backup DDN through the AUX port dialing, and ping each other between 1751 and 3662 with little packet loss; the wks that Ping lan B on vrouters 1751 are normal. The Ethernet port of the Ping1751 vro on A LAN destination (connect LAN A, and A connects only one host through the crossover line) it is also normal. However, when a lan a's workstation ping lan B's workstation, it can only Ping A limited number of times, and then packet loss begins.

Diagnosis Process

The author first analyzes several possible problems:

(1) The cross line is too bad, and the quality is too low.

(2) the duplex mode of the network device does not match.

(3) The nic of host a may be faulty.

After checking one by one, no problem is found. ping lan B once on LAN A and then show fast switching to AUX port-packet drop

Then you cannot Ping it.

Run the show int async command to View Details:

show int a5 Async5 is up, line protocol is up Hardware is Async Serial MTU 1500 bytes, BW115 Kb it, DLY 100000 usec reliability 254/255, txioad 1/255, rxioad 1/255 Encapsulation PPP, loopback not set DTR is pulsed for 5 seconds on reset Time to interface disconnect: idle 00:02:59 LCP Open Open: IPCP Last input 00:01:41, output 00:01:41, output hang never Last clearing of "show interface" counters 03:52:24 Input queue: 1/75/0/0 (size/max/drops/f lushes); Total output drops: 0 Queueing strategy: weighted fair Output queue: 0/1000/64/0 (size/max total/threshold/drops) Conversations 0/1/16 (active/max active/max total) Reserved Conversations 0/0 (allocated/max allocated) Available Bandwidth 86 kilobits/sec 5 minute input rate 0 bits/sec, 0 packets/sec 5 minute output rate 0 bits/sec, 0 packets/sec 297 packets input, 22847 bytes, 0 no buffer Received 0 broadcasts, 0 runts, 0 giants, 0 throttles 5 input errors, 5 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort 312 packets output, 23822 bytes, 0 underruns 0 output errors, 0 collisions, 6 interface resets 0 output buffer failures, 0 output buffers swapped out 0 carrier transitions

I didn't see any problems from here. I finally thought that the AUX port may not support fast forwarding. perform the following operations:

First, in the global configuration mode of 1751:

no ip cef

Then, each interface is as follows:

No ip route-cache (disable port fast forwarding)

Finally, on int async:

no ip route-cache

After fast switching is disabled, the problem is solved.

1. Use the aux port to connect two vrouters back-to-back