Need clarification on ARP

[kgraman86]

Dear  all,..

As a matter of fact i am new to this field .I have cisco 1700 series router which has ea0 and FE 0 port

E0 connected to LAN and FA0 for ISP ,both are configured wit publisc ip.and ststic route to ISP.

(E0 connected to switch and fa0 connected to ISP MUX)

When i issued sho arp command i have received  more than 30 entries of  MAC and IP  address .

I am wondering how i received this much mac in arp table.

Thanks in advance

[Muhammad Thanveer]

Hello Govindaraman,

If the interface shown in the output command is E0 then the arp entries are your local lan ips.

your output should look osmething like this,

Router#sh ip arp

Protocol  Address          Age (min)  Hardware Addr   Type   Interface

Internet  10.1.1.1                -   0090.215C.D701  ARPA          E0

Internet  10.1.1.3                0   000C.850A.93A7  ARPA          E0

Please rate helpful posts

Regards
Thanveer
"Everybody is genius. But if you judge a fish by its ability to climb a tree, it will live its whole life believing that it is a stupid."

[Richard Burts · Accepted solution]

Since both interfaces on the router are Ethernet interfaces then both interfaces process ARP and some of the entries in the ARP table should be from E0 and some from FA0.

It would be logical that there would be an entry in the ARP table for each of the devices of the inside network. You do not tell us how many devices are in the network connected through the switch to the E0. So we do not know whether 30 entries is reasonable or not. If there are 30 devices in the network then 30 entries in the ARP table is what is expected.

If the number of devices of the inside network is less than 30 then there may be another explanation for the number of entries in the ARP table. The original poster says that there is a static route. It is possible that additional ARP entries are caused by the operation of the static route. Is the static route something like this:

ip route 0.0.0.0 0.0.0.0 FA0

If it is then the router will need to ARP for every remote destination and that can lead to quite large ARP tables.

HTH

Rick

[kgraman86]

Dear richard ,

thanks a lot.

I have less than 30 devices in my LAN.i belive static route only caused this .

(It is possible that additional ARP entries are caused by the  operation of the static route. Is the static route something like this:

ip route 0.0.0.0 0.0.0.0 FA0

If it is then the router will need to ARP for every remote destination and that can lead to quite large ARP tables.)

Thank you so much for your reply

[Richard Burts]

I am glad that you found my answer helpful. Thank you for using the rating system to mark this question as answered. It makes the forum more useful when people can read a question and can know that a correct answer was found. Your marking has contributed to this process.

HTH

Rick

[kgraman86]

hai muhammad,

i got around 30 entries and all the ip's are public.