CODEWITHSUNDEEP
snmp
rocky
rocky

Reputation: 81

snmp network discovery identify mac address of device connected to a router

i am working on a network discovery program which employs snmp to discover devices in the network. My program takes the router-ip as input, scans the iprotetable(iprouttenext hop),to determine if any other routers are connected to it. for non router devices (like switch) the algorithm scans the arptable (ipnettomediatable) of the router, but cant find the connected switch unless i ping from the switch to the router. is there any way where i can determine the device connected directly to the router ..?

Upvotes: 0

Views: 1781

Answers (2)

TeeTee
TeeTee

Reputation: 46

Getting the devices connected to a router or switch is not that easy. Switches usually maintain a MAC forwarding database where it stores which MAC address has been seen on which switch port. This table can be easily read by using the bridge MIB. Unfortunately, there are several issues to take care of:

  1. Those entries disappear again, when a device to the switch has been switched off or is simply not communicating. Usually, the entries in the MAC forwarding tables age out after 5 minutes or so.
  2. The fact that a MAC address has been seen on a switch port doesn't mean that the device having the mac address is directly connected to the port. There might be any number of other switches, routers or hubs inbetween.

Some manufacturers like Cisco or HP use their own protocols to determine the network topology. There are several protocols (that area usually also available through a SNMP MIB):

  1. CDP (Cisco Discovery Protocol): This is a proprietary protocol developed by Cisco to expose network topology information. Some vendors licensed this technology and implement that protocol in their products.
  2. LLDP (Link Layer Discovery Protocol): A standard similar to CDP, but without paying Cisco license fees :-)
  3. And many more. I know kthat Extreme Networks has their own protocols and I am pretty sure that other vendors have them as well.

The problem with those protocols is when you have a mixed environment. Cisco switches talking CDP do not understand Extremen Network's protocol and vica versa.

If your goal is to find IP addresses to discover, then you might use the ARP caches for routers. Scanning the ARP caches for switches makes no real sense, because they're operating on layer 2.

Upvotes: 2

tomm
tomm

Reputation: 302

I was using broadcast message for my java snmp agent

Upvotes: 0

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