KB ID 0001258
If you have a complicated network, you can spend more time finding out how it’s configured, than actually doing any work on it!
Today I had a client that needed some changes made on their LAN, I knew their name, and their network address, and common sense told me which of the core switches they were connected to.
A quick search on the client name told me what VRF they were in, and what VLAN they were in (3000), let’s have a look at that;
Petes-Core-SW#show run vlan 3000 Building configuration... Current configuration: ! vlan 3000 name CORP:NET end
That doesn’t yield much more than I already know, so I can either do this and get a LOT of information;
Petes-Core-SW#show interfaces vlan 3000 Vlan3000 is up, line protocol is up Hardware is EtherSVI, address is c062.6be3.3000 (bia c062.6be3.9d40) Description: CORP:NET Internet address is 192.168.1.100/24 MTU 1500 bytes, BW 1000000 Kbit, DLY 10 usec, reliability 255/255, txload 1/255, rxload 1/255 Encapsulation ARPA, loopback not set Keepalive not supported ARP type: ARPA, ARP Timeout 04:00:00 Last input 00:00:00, output never, output hang never Last clearing of "show interface" counters never Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0 Queueing strategy: fifo Output queue: 0/40 (size/max) 5 minute input rate 254000 bits/sec, 115 packets/sec 5 minute output rate 504000 bits/sec, 119 packets/sec L2 Switched: ucast: 22179333 pkt, 1561846492 bytes - mcast: 0 pkt, 0 bytes L3 in Switched: ucast: 471521755 pkt, 367932934560 bytes - mcast: 0 pkt, 0 bytes L3 out Switched: ucast: 493390206 pkt, 464908773459 bytes - mcast: 0 pkt, 0 bytes 475554223 packets input, 366284328453 bytes, 0 no buffer Received 0 broadcasts (1116 IP multicasts) 0 runts, 0 giants, 0 throttles 0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored 493591347 packets output, 462947525840 bytes, 0 underruns 0 output errors, 0 interface resets 0 output buffer failures, 0 output buffers swapped out
Or a more sensible;
Petes-Core-SW#show run interface vlan 3000 Building configuration... Current configuration : 160 bytes ! interface Vlan3000 description CORP:NET mac-address c062.6be3.3000 vrf forwarding CORP:NET ip address 192.168.1.100 255.255.255.0 end
Find What VLAN An IP Address Is In
If you have the opposite problem, i.e. you know the IP, (or a part of the IP). You can get the VLAN number like so;
Petes-Core-SW#show ip int br | incl 192.168.1.100 Vlan3000 192.168.1.100 YES NVRAM up up
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