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Protocol status incorrect #33
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Thanks for reporting. =) I'm able to reproduce it:
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After analyzing a packet capture of the serial link there is a keep-alive packet (cHDLC, SLARP) that is sent between the routers and used to know if the line is up. Relying on this packet means it will report line down on timeout, which explains the delay of the message in the other router. |
After analyzing a packet capture of the ethernet link there are CDP packets sent every 62 seconds (with 180 timeout) and LOOP packets sent every 10 seconds. Playing around with the configs:
Apparently it doesn't decide the ethernet line status from the traffic. Next step: how does the ethernet card report the line status? how does the ethernet card know that the interface is administratively down ( |
I could be totally wrong here, but I believe that a physical router detects LIPs are also used to determine speed/duplex negotiation, and again this is But good luck! On 5 April 2014 13:32, Flávio J. Saraiva notifications@github.com wrote:
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Yes, a real ethernet card detects link up/down from the physical state. But I'm not sure how it informs the software driver of the change in status. =~~ Indeed we don't emulate the physical layer. However we can still fake a link up/down if we rely on the fact that IOS sends periodic packets. (must be configurable since these packets can be disabled) |
Cisco routers send LOOP packets every 10 seconds on Ethernet interfaces (I However, you can't really rely on an interface seeing LOOPS from another IF however you KNEW it was a point-to-point connection between two routers, But LOOPS are the only packet you can RELY on - all others can be turned Other cases - like directly connected to a host (VPCS) or Qemu/ASA/Virtual Chris On 7 April 2014 07:33, Flávio J. Saraiva notifications@github.com wrote:
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Yes, as you point out, it's not completely reliable in any scenario. That's why I was thinking of leaving it off by default (configurable in each nio). In my view any traffic received would indicate the link is still active, even an empty packet, and a configurable timeout time with no packets received would indicate link down. My concern is... would it ever be used? |
Related topic: http://forum.gns3.net/topic9324.html |
I wouldn't do timeout based on packet events as to up/down. It's better to leave it up than false positive if you can't do event based detection on the far side. |
@flaviojs After 4 years, up to this post. There is a problem with the fact that interfaces are always up/line protocol up : I've got this problem yesterday, i had one link between two routers, and those two routers were connected to a local vlan (switch + pc). problem, one router is active (HSRP), but when the link between him and the local vlan is removed, the interface/line protocol are still up, so routing table don't update, so he don't know that he can go to the local vlan via the second router. |
Detecting the protocol down (shutting down the remote interface) on etheret interfaces does not work.
Turning down the interface fa1/0 should result in a "Protocol down" on interface fa0/0. But this behavior does only work on serial interfaces.
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