Say if there are two static route to isp and if one fails how does the other link send the remaining data & even if the data is continued from very much same point of failure. Will the assembly of the packets will be a a success?

  • If an interface goes down, any route in the routing table for that interface will be withdrawn from the routing table. That is one possibility of a failing route. There is also the possibility to use IPSLA to remove routes that fail in other ways. – Ron Maupin Aug 8 '18 at 14:45
  • Thanks Ron for the reply. :) .. So what about the data re-assembly on the receiving end ? – Ethernet Aug 8 '18 at 14:49
  • I really do not understand your question about re-assembly of packets. That only happens if packet must be fragmented, but in the modern world, most sites will not accept packets fragments in order to avoid DoS attacks based on fragmentation. We now use PMTUD to discover the proper path MTU before sending packets. – Ron Maupin Aug 8 '18 at 14:56

The problem with static routes is that the router doesn't know if the link fails. So the router will continue to forward packets out the failed link, and they will be lost.

If there are two equal routes in the routing table, then the router will alternate paths and you'll lose every other packet.

It's up to the end host to determine that data is lost and either timeout or request retransmission.

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  • Hi Ron.. thanks for the reply. Even if I add a floating static route will it not work? I tested this few months back & I think data started going through backup link but I don't know if reassembly will be a success. What do you say? – Ethernet Aug 8 '18 at 13:34
  • If the outgoing interface is down, then the primary route will be removed. But there are lots of cases where the route fails, but the interface stays up. But again, it's up to the end host to detect missing data and recover. The router plays no part in that. – Ron Trunk Aug 8 '18 at 14:48

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