Depends on several factors, including nuances I've skipped over in the response below.
If the physical layer or data link layer protocol indicates the link is down, the route will be disabled. If there is no keepalive mechanism, yes, ARP will come into play. That's one of the minor but important roles for routing protocols when you don't think you need one -- failure detection on media types without a layer 3 hello mechanism. There is a good deal of research going on involving lightweight signaling protocols to detect such failures without the overhead of a full routing protocol, especially with respect to MPLS. Next, what happens will depend on the switching and load balancing mode in use. If the two interfaces are per-packet load balanced, traffic will move quickly to the remaining route. If they are CEF source-destination balanced, the FIB entry for the down route will be flushed and the traffic diverted, again quickly. If they are per-destination load balanced, it depends further. Either R2 or R3 will have been cached as the path to 10.1.1.0/24. If R2 was the selected path, R3 is idle and vice versa. If R3 had been selected, there would be no impact on traffic. If it was R2, however, once the IOS detected the router was down, the interface cache would be invalidated, and a new interface selected with the next packet to that destination. >it will still send traffic to both until the ARP cache times out, then it will >drop half. i don't know the Cisco ARP timeout. > > >vr4drvr . wrote: > >> Here's a static routing question that I need answered. I do have theories, >> but I need a proof positive answer. Simple scenario. >> >> R2---10.1.1.0/24 >> R1----| >> R3---10.1.1.0/24 >> >> 3 routers are connected to an ethernet segment. R1 has 2 static routes to >> the 10.1.1.0/24 network pointing to the IP address of the next hop ethernets >> on R2 and R3, thereby providing load balancing and fault tolerance. My >> question is... if an ethernet interface on R2 was to go down, how does that >> affect the routing from R1 to the 10.1.1.0 network? For instance, will R1 >> drop half the traffic? How does the ARP cache on R1 impact routing, or >> rather, how is routing impacted by the ARP cache? Will the static route >> through R2 get dropped so to speak? >> >> TIA. >> >> _________________________________________________________________ >> Join the worlds largest e-mail service with MSN Hotmail. >> http://www.hotmail.com Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=29842&t=29842 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
