András, I don't think I'll see such cable at nowadays :) However, thank you for explaining this!
regards, martin 2011/8/1 Tóth András <[email protected]>: > Hi Martin, > > I cannot comment on the 2900 switches, as it's very old and not > supported anyway by Cisco. On the 2950 switches, when keepalives are > enabled and looping condition is detected, the interface will be > err-disabled, this is an expected behavior. For more information, > please visit the below documentations. > > Refer to the "Loopback error" section on the following link: > http://www.cisco.com/en/US/tech/tk389/tk621/technologies_tech_note09186a00806cd87b.shtml > > Refer to the "%ETHCNTR-3-LOOP_BACK_DETECTED : Keepalive packet > loop-back detected on [chars]" section here: > http://www.cisco.com/en/US/products/hw/switches/ps700/products_tech_note09186a00801b42bf.shtml#prob1b > > I guess you can read more about Type 2 cabling on the following link. > http://www.cisco.com/en/US/products/hw/gatecont/ps2250/products_tech_note09186a008009452e.shtml#ii > > Best regards, > Andras > > > 2011/7/31 Martin T <[email protected]>: >> 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/
