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Null Packets

DEar All,

I am running show ip cache flow command on Router . I am attaching the output fo same ..

For DstIf , NULL is appearing with DstIP address as Broadcast Ip address of LAN.

Why is this happening? What could be the cause & remedy for same .?

regds,

aman

1 REPLY
Hall of Fame Super Silver

Re: Null Packets

Aman

You seem to think that this is a problem, but it is in fact a normal behavior. We can explain the cause and there is no need for any remedy.

I have included one line from your output as an example. What this shows is that some device at address 10.192.48.35 on interface FastEthernet0/1 send a broadcast packet which was received by the router. Since routers do not forward broadcasts the router will discard this packet which is indicated by the destination of null.

Fa0/1 10.192.48.35 Null 10.192.48.255 11 0089 0089 3

It might help if we recognize that the source port and destination port are given in hex. The hex value of 89 is a decimal value of 137. So we can see that the packets here were broadcast NetBIOS packets which the router does not forward.

So this is normal behavior and not a problem.

HTH

Rick

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