András, under IOS one can configure "keepalive" settings of Fa/Gi/Te interfaces of Cisco 4500 and Fa ports of Cisco 2900 series as well, but as much as I tested with 2900 series, while keepalive frames are actually sent, in case of loop(I made a RJ45 hardware loop), the port is not shut down.
On the other hand, in case of Cisco 2950, the keepalive frame indeed forced port to "err-disabled" state when I plugged my RJ45 hardware-loop into the port: 00:06:53: %SYS-5-CONFIG_I: Configured from console by console 00:06:55: %ETHCNTR-3-LOOP_BACK_DETECTED: Keepalive packet loop-back detected on FastEthernet0/2. 00:06:55: %PM-4-ERR_DISABLE: loopback error detected on Fa0/2, putting Fa0/2 in err-disable state 00:06:56: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/2, changed state to down 00:06:57: %LINK-3-UPDOWN: Interface FastEthernet0/2, changed state to down When I set "no keepalive" to this very same switch port under C2950 and connect the same RJ45 hardware loop, the port stayed up. By "Type 2" cabling you mean so-called "Cat2"(Two shielded twisted pairs + four voice grade twisted pairs) cabling? And the idea is that in case there is a loop on physical layer, the switch port receives a keepalive frame with it's own MAC address as a destination and source address and shuts down the port? In the light of modern cabling standards, the "keepalive" feature isn't very useful, is it? regards, martin 2011/7/31 Tóth András <[email protected]>: > Hi Martin, > > Keepalives are sent on the Catalyst 2940, 2950, 2950-LRE, 2955, 2970, > 3550, 3560 or 3750 switch to prevent loops in the network. The primary > reason for the keepalives is to prevent loops as a result of Type 2 > cabling which does cause a loop in some situations. A loop is detected > when the switch receives back it's own keepalive pakcet. > > Keepalives are sent on ALL interfaces by default in 12.1EA based > software. Starting in 12.2SE based releases, keepalives are NO longer > sent by default on fiber and uplink interfaces. > > Best regards, > Andras > > > On Sun, Jul 31, 2011 at 3:51 AM, Martin T <[email protected]> wrote: >> 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 >> _______________________________________________ >> cisco-nsp mailing list [email protected] >> https://puck.nether.net/mailman/listinfo/cisco-nsp >> archive at http://puck.nether.net/pipermail/cisco-nsp/ >> > _______________________________________________ cisco-nsp mailing list [email protected] https://puck.nether.net/mailman/listinfo/cisco-nsp archive at http://puck.nether.net/pipermail/cisco-nsp/
