I have a following connection:
T60[eth0] <-> [Fa0/2]WS-C2950C-24
..and port Fa0/2 in the switch in configured like this:
WS-C2950C-24#sh run int Fa0/2
Building configuration...
Current configuration : 149 bytes
!
interface FastEthernet0/2
description -> T60
switchport mode access
switchport nonegotiate
no cdp enable
spanning-tree bpdufilter enable
end
WS-C2950C-24#
..and "keepalive" signals are sent after every 10s:
WS-C2950C-24#sh int Fa0/2 | i Keepalive
Keepalive set (10 sec)
WS-C2950C-24#
Now if I tcpdump those frames, they look like this:
root@martin-ThinkPad-T60:~# tcpdump -i eth0 -e -XX -c 4
tcpdump: WARNING: eth0: no IPv4 address assigned
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on eth0, link-type EN10MB (Ethernet), capture size 65535 bytes
03:26:35.984629 00:12:7f:13:8f:c2 (oui Unknown) > 00:12:7f:13:8f:c2
(oui Unknown), ethertype Loopback (0x9000), length 60:
0x0000: 0012 7f13 8fc2 0012 7f13 8fc2 9000 0000 ................
0x0010: 0100 0000 0000 0000 0000 0000 0000 0000 ................
0x0020: 0000 0000 0000 0000 0000 0000 0000 0000 ................
0x0030: 0000 0000 0000 0000 0000 0000 ............
03:26:45.984971 00:12:7f:13:8f:c2 (oui Unknown) > 00:12:7f:13:8f:c2
(oui Unknown), ethertype Loopback (0x9000), length 60:
0x0000: 0012 7f13 8fc2 0012 7f13 8fc2 9000 0000 ................
0x0010: 0100 0000 0000 0000 0000 0000 0000 0000 ................
0x0020: 0000 0000 0000 0000 0000 0000 0000 0000 ................
0x0030: 0000 0000 0000 0000 0000 0000 ............
03:26:55.984277 00:12:7f:13:8f:c2 (oui Unknown) > 00:12:7f:13:8f:c2
(oui Unknown), ethertype Loopback (0x9000), length 60:
0x0000: 0012 7f13 8fc2 0012 7f13 8fc2 9000 0000 ................
0x0010: 0100 0000 0000 0000 0000 0000 0000 0000 ................
0x0020: 0000 0000 0000 0000 0000 0000 0000 0000 ................
0x0030: 0000 0000 0000 0000 0000 0000 ............
03:27:05.984651 00:12:7f:13:8f:c2 (oui Unknown) > 00:12:7f:13:8f:c2
(oui Unknown), ethertype Loopback (0x9000), length 60:
0x0000: 0012 7f13 8fc2 0012 7f13 8fc2 9000 0000 ................
0x0010: 0100 0000 0000 0000 0000 0000 0000 0000 ................
0x0020: 0000 0000 0000 0000 0000 0000 0000 0000 ................
0x0030: 0000 0000 0000 0000 0000 0000 ............
4 packets captured
4 packets received by filter
0 packets dropped by kernel
root@martin-ThinkPad-T60:~#
As you can see, they are sent by switch port after every 10s. The
source and destination MAC address are the same and ethertype is
0x9000 and it looks like the frame is just padded with zeros. I can
change the keepalive messages interval between 1s and 32767s or
disable keepalive frames by "no keepalive" or "keepalive 0".
What are those "keepalive" frames used for? Some historical
configuration setting? What should my T60 NIC do with those frames as
at the moment it responds nothing?
regards,
martin
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