How to detect availability
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Posted by Igor Mamuzic on July 5, 2005, 1:11 pm
Please log in for more thread options - R1 ---- R2 ----- R3-----Internet How to make that R1 knows that the link between R2 and R3 is down? This is about Internet connection and R1 can't receive default route via routing protocol from my ISP, since some users that use R1 as default gateway are routed via another router (not shown above) using routing table (default route) and other users are routed to the Internet using policy routing (route-map). Best Regards, Igor | ||||||||||||||||||||||||||||
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Posted by Walter Roberson on July 5, 2005, 2:08 pm
Please log in for more thread options :- R1 ---- R2 ----- R3-----Internet :How to make that R1 knows that the link between R2 and R3 is down? How to make R1 know that the link between R1 and R2 is down? First you have to define "down". Do you mean only that the link has been cut (e.g., unplugged, a cable broke, a repeater burned out, a laser transceiver burned out), or do you mean that the link is not passing *usable* data (e.g., DoS attack is using the entire bandwidth), or do you mean that the link isn't passing *any* data (e.g., equipment is wedged but carrier is there), or do you include the case where the link quality has dropped to the point where the throughput is below some quality measure (e.g., a fibre connection got dirty or a cable is frayed or there is a ground fault or a duplex mismatch) ? Do you really care whether it is the link R2 - R3 that is down, or are you really concerned with whether R1 can get data to R3 ? It makes a difference if, for example, there is an unshown redundant connection between R1 and R3, or if R1 is just a monitoring device and all the important data is joining the topology at R2. If the concern is getting data between R1 and R3, then ping R3... For more advanced methods with various tradeoffs, see Vincent C. Jones' book about High Availability Networking Using Cisco Routers. -- Ceci, ce n'est pas une idée. | ||||||||||||||||||||||||||||
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Posted by Ivan Ostres on July 5, 2005, 3:46 pm
Please log in for more thread options One way would be to use routing protocol and create a loopback on R1 and announce it in mentioned routing protocol. If route to that "network" is not available at R1, that should mean that R1 has no connectivity to R3. -- Ivan *** User rot13 to see my eMail address *** | ||||||||||||||||||||||||||||
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Posted by toby on July 6, 2005, 2:15 pm
Please log in for more thread options
>> I have the following topology:
>> >> - R1 ---- R2 ----- R3-----Internet >> >> How to make that R1 knows that the link between R2 and R3 is down? This >> is >> about Internet connection and R1 can't receive default route via routing >> protocol from my ISP, since some users that use R1 as default gateway are >> routed via another router (not shown above) using routing table (default >> route) and other users are routed to the Internet using policy routing >> (route-map). >> >
Hi Ivan
> One way would be to use routing protocol and create a loopback on R1 and > announce it in mentioned routing protocol. If route to that "network" is > not available at R1, that should mean that R1 has no connectivity to R3. > > > -- > Ivan > I have been trying to achieve this in my lab since this was posted and so far have failed. Can you expand on your idea? I have used the below topology. R1----R2----R3---R4 | | R5----------- Traffic can come from 2 source ip addresses on R1 (and i'm not interested in return traffic at this stage) and in my lab terminate on R5 loopback address R2 has a route map on the interface from R1 so certain source addresses route to R5's loopback route through R3-R4-R5 other source addresses use R2-R5 by default. (I am using OSPF over the network and have tweaked the bandwidth on links to ensure traffic for R5 route viaR4 from R3). What the original poster is querying and me too now is that as the routemap on R2 uses a next hop for certain source addresses from R1. How can we tweak the config so that traffic entering R2 from R1 does not use the route-map when the link from R3-R4 is down. i.e. to stop this traffic wasting bandwidth between R2-R3 just to be routed back to R2 and onward to R5. My initial thought was to set the next hop in the route-map to an address of the R4 Interface but as this is not strictly the next hop all I get is hits on the route-map but the routing is ignored via the set statement. Is there a way to detect distant link failures to stop this bandwidth wastage. Regards Toby | ||||||||||||||||||||||||||||
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Posted by Igor Mamuzic on July 7, 2005, 8:16 am
Please log in for more thread options Ivan,
Did you mean to create loopback interface on R1 as a placeholder for this network and then redistribute it into RIP? If so, I'm already have it at R1 since this lo is my placeholder for sending my network into ISP with RIP. ISP router is R2 on my topology "drawing". When R2 looses RIP updates from me (R1) then my ISP knows that it must route traffic destined for my network via alternative path which works good. The problem is that R1 is default gateway for several internal networks and using route-map it routes one internal network via RIP to the ISP (R2) and uses default route from ISP's OSPF router (not show on this topology) to route second internal network. I'm seeking for a solution which will enable R1 to reroute traffic originally routed with route-map to default gateway in routing table (OSPF) in the case that path to the Internet via R2 is down. R2 is connected with my R1 with UTP cabling, but R2 and R3 are connected with wireless link, so that I'm not worried about loosing connectivity between R2 and R1, but between R2 and R3. If the communication between R2 and R3 is lost my route-map (on R1) will still forward packers to R2 (which is black hole), since route-map next-hop (R2) is still in the R1's routing table. Best Regards, Igor >> I have the following topology:
>> >> - R1 ---- R2 ----- R3-----Internet >> >> How to make that R1 knows that the link between R2 and R3 is down? This >> is >> about Internet connection and R1 can't receive default route via routing >> protocol from my ISP, since some users that use R1 as default gateway are >> routed via another router (not shown above) using routing table (default >> route) and other users are routed to the Internet using policy routing >> (route-map). >> >
> One way would be to use routing protocol and create a loopback on R1 and > announce it in mentioned routing protocol. If route to that "network" is > not available at R1, that should mean that R1 has no connectivity to R3. > > > -- > Ivan > > *** User rot13 to see my eMail address *** | ||||||||||||||||||||||||||||
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>
> - R1 ---- R2 ----- R3-----Internet
>
> How to make that R1 knows that the link between R2 and R3 is down? This is
> about Internet connection and R1 can't receive default route via routing
> protocol from my ISP, since some users that use R1 as default gateway are
> routed via another router (not shown above) using routing table (default
> route) and other users are routed to the Internet using policy routing
> (route-map).
>