Ever wondered what switch or router port your server was plugged into? If your server is plugged into a Cisco switch or router, then chances are it is broadcasting Cisco Discovery Protocol packets periodically. Other vendors use LLDP (ethertype 0x88cc). You can use tshark to capture one of these packets on a physical server (CDP does not usually pass through to virtual machines) and determine what port you are plugged into.
Note that Cisco ASA firewalls do not support CDP, so if your server is plugged into an ASA, this tip won't do you any good. If you find yourself on a VMware ESXi server, it does not come with tshark installed; however, you can use the following command instead:
vim-cmd hostsvc/net/query_networkhint
tshark -i eth0 -V -f "ether host 01:00:0c:cc:cc:cc or ether proto 0x88cc" -c 2
Running as user "root" and group "root". This could be dangerous.
Capturing on eth0
Frame 1 (482 bytes on wire, 482 bytes captured)
Arrival Time: Apr 20, 2011 00:45:32.663667000
[Time delta from previous captured frame: 0.000000000 seconds]
[Time delta from previous displayed frame: 0.000000000 seconds]
[Time since reference or first frame: 0.000000000 seconds]
Frame Number: 1
Frame Length: 482 bytes
Capture Length: 482 bytes
[Frame is marked: False]
[Protocols in frame: eth:llc:cdp:data]
IEEE 802.3 Ethernet
Destination: 01:00:0c:cc:cc:cc (01:00:0c:cc:cc:cc)
Address: 01:00:0c:cc:cc:cc (01:00:0c:cc:cc:cc)
.... ...1 .... .... .... .... = IG bit: Group address (multicast/broadcast)
.... ..0. .... .... .... .... = LG bit: Globally unique address (factory default)
Source: 00:1a:2f:4b:bb:23 (00:1a:2f:4b:bb:23)
Address: 00:1a:2f:4b:bb:23 (00:1a:2f:4b:bb:23)
.... ...0 .... .... .... .... = IG bit: Individual address (unicast)
.... ..0. .... .... .... .... = LG bit: Globally unique address (factory default)
Length: 468
Logical-Link Control
DSAP: SNAP (0xaa)
IG Bit: Individual
SSAP: SNAP (0xaa)
CR Bit: Command
Control field: U, func=UI (0x03)
000. 00.. = Command: Unnumbered Information (0x00)
.... ..11 = Frame type: Unnumbered frame (0x03)
Organization Code: Cisco (0x00000c)
PID: CDP (0x2000)
Cisco Discovery Protocol
Version: 2
TTL: 180 seconds
Checksum: 0x6547 [correct]
[Good: True]
[Bad : False]
Device ID: INITECH-FLOOR1SW1.initech.com
Type: Device ID (0x0001)
Length: 33
Device ID: INITECH-FLOOR1SW1.initech.com
Software Version
Type: Software version (0x0005)
Length: 247
Software Version: Cisco IOS Software, C3750 Software (C3750-IPBASEK9-M), Version 12.2(50)SE3, RELEASE SOFTWARE (fc1)
Technical Support: http://www.cisco.com/techsupport
Copyright (c) 1986-2009 by Cisco Systems, Inc.
Compiled Wed 22-Jul-09 06:19 by prod_rel_team
Platform: cisco WS-C3750G-48TS
Type: Platform (0x0006)
Length: 24
Platform: cisco WS-C3750G-48TS
Addresses
Type: Addresses (0x0002)
Length: 17
Number of addresses: 1
IP address: 10.1.1.3
Protocol type: NLPID
Protocol length: 1
Protocol: IP
Address length: 4
IP address: 10.1.1.3
Port ID: GigabitEthernet2/0/35
Type: Port ID (0x0003)
Length: 25
Sent through Interface: GigabitEthernet2/0/35
Capabilities
Type: Capabilities (0x0004)
Length: 8
Capabilities: 0x00000028
.... .... .... .... .... .... .... ...0 = Not a Router
.... .... .... .... .... .... .... ..0. = Not a Transparent Bridge
.... .... .... .... .... .... .... .0.. = Not a Source Route Bridge
.... .... .... .... .... .... .... 1... = Is a Switch
.... .... .... .... .... .... ...0 .... = Not a Host
.... .... .... .... .... .... ..1. .... = Is IGMP capable
.... .... .... .... .... .... .0.. .... = Not a Repeater
Protocol Hello: Cluster Management
Type: Protocol Hello (0x0008)
Length: 36
OUI: 0x00000C (Cisco)
Protocol ID: 0x0112 (Cluster Management)
Cluster Master IP: 0.0.0.0
UNKNOWN (IP?): 0xFFFFFFFF (255.255.255.255)
Version?: 0x01
Sub Version?: 0x02
Status?: 0x21
UNKNOWN: 0xFF
Cluster Commander MAC: 00:00:00:00:00:00
Switch's MAC: 00:16:c7:fb:bb:00
UNKNOWN: 0xFF
Management VLAN: 0
VTP Management Domain: INITECH_CORP
Type: VTP Management Domain (0x0009)
Length: 12
VTP Management Domain: INITECH_CORP
Native VLAN: 350
Type: Native VLAN (0x000a)
Length: 6
Native VLAN: 350
Duplex: Full
Type: Duplex (0x000b)
Length: 5
Duplex: Full
Trust Bitmap: 0x00
Type: Trust Bitmap (0x0012)
Length: 5
Trust Bitmap: 00
Untrusted port CoS: 0x00
Type: Untrusted Port CoS (0x0013)
Length: 5
Untrusted port CoS: 00
Management Addresses
Type: Management Address (0x0016)
Length: 17
Number of addresses: 1
IP address: 10.1.1.3
Protocol type: NLPID
Protocol length: 1
Protocol: IP
Address length: 4
IP address: 10.1.1.35
Power Available: 0 mW, 4294967295 mW
Type: Power Available (0x001a)
Length: 16
Request-ID: 0
Management-ID: 1
Power Available: 0 mW
Power Available: 4294967295 mW
Frame 2 (482 bytes on wire, 482 bytes captured)
Arrival Time: Apr 20, 2011 00:46:32.674563000
[Time delta from previous captured frame: 60.010896000 seconds]
[Time delta from previous displayed frame: 60.010896000 seconds]
[Time since reference or first frame: 60.010896000 seconds]
Frame Number: 2
Frame Length: 482 bytes
Capture Length: 482 bytes
[Frame is marked: False]
[Protocols in frame: eth:llc:cdp:data]
IEEE 802.3 Ethernet
Destination: 01:00:0c:cc:cc:cc (01:00:0c:cc:cc:cc)
Address: 01:00:0c:cc:cc:cc (01:00:0c:cc:cc:cc)
.... ...1 .... .... .... .... = IG bit: Group address (multicast/broadcast)
.... ..0. .... .... .... .... = LG bit: Globally unique address (factory default)
Source: 00:1a:2f:4b:bb:23 (00:1a:2f:4b:bb:23)
Address: 00:1a:2f:4b:bb:23 (00:1a:2f:4b:bb:23)
.... ...0 .... .... .... .... = IG bit: Individual address (unicast)
.... ..0. .... .... .... .... = LG bit: Globally unique address (factory default)
Length: 468
Logical-Link Control
DSAP: SNAP (0xaa)
IG Bit: Individual
SSAP: SNAP (0xaa)
CR Bit: Command
Control field: U, func=UI (0x03)
000. 00.. = Command: Unnumbered Information (0x00)
.... ..11 = Frame type: Unnumbered frame (0x03)
Organization Code: Cisco (0x00000c)
PID: CDP (0x2000)
Cisco Discovery Protocol
Version: 2
TTL: 180 seconds
Checksum: 0x6547 [correct]
[Good: True]
[Bad : False]
Device ID: INITECH-FLOOR1SW1.initech.com
Type: Device ID (0x0001)
Length: 33
Device ID: INITECH-FLOOR1SW1.initech.com
Software Version
Type: Software version (0x0005)
Length: 247
Software Version: Cisco IOS Software, C3750 Software (C3750-IPBASEK9-M), Version 12.2(50)SE3, RELEASE SOFTWARE (fc1)
Technical Support: http://www.cisco.com/techsupport
Copyright (c) 1986-2009 by Cisco Systems, Inc.
Compiled Wed 22-Jul-09 06:19 by prod_rel_team
Platform: cisco WS-C3750G-48TS
Type: Platform (0x0006)
Length: 24
Platform: cisco WS-C3750G-48TS
Addresses
Type: Addresses (0x0002)
Length: 17
Number of addresses: 1
IP address: 10.1.1.3
Protocol type: NLPID
Protocol length: 1
Protocol: IP
Address length: 4
IP address: 10.1.1.3
Port ID: GigabitEthernet2/0/35
Type: Port ID (0x0003)
Length: 25
Sent through Interface: GigabitEthernet2/0/35
Capabilities
Type: Capabilities (0x0004)
Length: 8
Capabilities: 0x00000028
.... .... .... .... .... .... .... ...0 = Not a Router
.... .... .... .... .... .... .... ..0. = Not a Transparent Bridge
.... .... .... .... .... .... .... .0.. = Not a Source Route Bridge
.... .... .... .... .... .... .... 1... = Is a Switch
.... .... .... .... .... .... ...0 .... = Not a Host
.... .... .... .... .... .... ..1. .... = Is IGMP capable
.... .... .... .... .... .... .0.. .... = Not a Repeater
Protocol Hello: Cluster Management
Type: Protocol Hello (0x0008)
Length: 36
OUI: 0x00000C (Cisco)
Protocol ID: 0x0112 (Cluster Management)
Cluster Master IP: 0.0.0.0
UNKNOWN (IP?): 0xFFFFFFFF (255.255.255.255)
Version?: 0x01
Sub Version?: 0x02
Status?: 0x21
UNKNOWN: 0xFF
Cluster Commander MAC: 00:00:00:00:00:00
Switch's MAC: 00:16:c7:fb:bb:00
UNKNOWN: 0xFF
Management VLAN: 0
VTP Management Domain: INITECH_CORP
Type: VTP Management Domain (0x0009)
Length: 12
VTP Management Domain: INITECH_CORP
Native VLAN: 350
Type: Native VLAN (0x000a)
Length: 6
Native VLAN: 350
Duplex: Full
Type: Duplex (0x000b)
Length: 5
Duplex: Full
Trust Bitmap: 0x00
Type: Trust Bitmap (0x0012)
Length: 5
Trust Bitmap: 00
Untrusted port CoS: 0x00
Type: Untrusted Port CoS (0x0013)
Length: 5
Untrusted port CoS: 00
Management Addresses
Type: Management Address (0x0016)
Length: 17
Number of addresses: 1
IP address: 10.1.1.35
Protocol type: NLPID
Protocol length: 1
Protocol: IP
Address length: 4
IP address: 10.1.1.3
Power Available: 0 mW, 4294967295 mW
Type: Power Available (0x001a)
Length: 16
Request-ID: 0
Management-ID: 1
Power Available: 0 mW
Power Available: 4294967295 mW
2 packets captured
In the example above, our server is plugged into switch port GigabitEthernet2/0/35 on the switch with the hostname INITECH-FLOOR1SW1.initech.com