10 Replies Latest reply: May 2, 2012 6:49 PM by Patrick Geschwindner - CCIE R&S, CCSI RSS

    Dynamically changing paths decisions

    sparky

      Background:

       

      We have a hub and spoke vpn topology, we (i am) located at the data center, we spoke out via VPN (EIGRP over GRE tunnels) to our partners (located all around the world) currently not every vpn router is running EIGRP, but we are slowly getting there (but for the sake of this, lets say they all run EIGRP)...

       

      current.png

       

       

       

      Scenario

      Since we have all these connections and they are all interlinked via the datacenter, could we mesh them so that each site gets the BEST possible path to each other,

       

      So, I see it as:

       

      proposal.png

      BUT ..... the problem being say we have some high latency that has just appeared from no where on the link between China --> Italy and this link connecting them was the primary (sucessor) it wouldn't be enough for a topology change and for the next best route to kick in (fessiable successor) say via the datacenter ...

       

      My main problem is, i cant see how to get each spoke to dynamically change if a problem say with the link was to start (like latency, not a downed link) so therefore the next best route wont be selected ....

       

       

      Question:

      With all the routing protocols (that i am familar with, EIGRP, OSPF and some BGP), i cant see how i would overcome this problem, as the algorithm (wheather it be DUAL or Dijkstra etc) would only do this when the router first forms the neighbour (or a topology change) it wont constantly monitor the links checking latency etc and then change accordingly

       

      Am i wrong, or is there another solution?

        • 1. Re: Dynamically changing paths decisions
          Cristian F. Stoica

          Sparky, have a look at the IP SLA feature.

          • 2. Re: Dynamically changing paths decisions
            piperflyer

            You may also want to look into what EIGRP can do with the LOAD value when calculating its metric.  This is a value that is updated in real time.  I have only heard of one real-world organizaiton doing this though.  It is generally a bad idea to re-converge your network during times of high load.  SLA may be the way to go, possibly combined with PfR.

            • 3. Re: Dynamically changing paths decisions
              sparky

              Cheers guys, PFR looks pretty smart   ..... going to need to have a good look into this, it could be the answer

              • 4. Re: Dynamically changing paths decisions
                Nuno

                Hi,

                 

                if i understand right,

                 

                 

                sparky wrote:

                Scenario

                Since we have all these connections and they are all interlinked via the datacenter, could we mesh them so that each site gets the BEST possible path to each other,

                 

                So, I see it as:

                 

                proposal.png


                 

                it depends on the circuites you have leased from your ISP. If your datacenter is the Hub on that topology you dont have much to do, as all the paths require that you pass through the Hub (datacenter) circuite. If you aquire other circuites Independantly from your ISP you can then apply Policy Base Routing, SLA monitoring and best path selection and load balancing which in my opinion EIGRP is the best IGP to go for, but i do not see the benifits of doing that if you only have 1 circuite from each partener to the datacenter meaning 4 Point-to-Point connections as they are all restricted to 1 path only.

                 

                Physically, how many circuites have your company bought or rented from the ISP? Which network type are they running? Hub and spoke, but which kind of network? Point-to-Point, Point-to-Multipoint, Multipoint? If you explain in more detail you are more likelly to be helped.

                 

                NL

                • 5. Re: Dynamically changing paths decisions
                  sparky

                  Sorry, i should have clarified, the VPN links are all over public internet  (fibre, xDSL)

                  • 6. Re: Dynamically changing paths decisions
                    Nuno

                    yes, i understand that, but which is the network type that they are linked?

                     

                    1 connection to each partener independantly and 1 connection from each partener to the datacenter, or you have 1 connection from each partener to the datacenter (hub and spoke point-to-point) topology and all links pass through the datacenter?

                     

                    Which circuites did your company rented from the ISP?

                    • 7. Re: Dynamically changing paths decisions
                      sparky

                      currently there is no connection between the vpn peers to each other, only to the data center ... see the first image

                      • 8. Re: Dynamically changing paths decisions
                        Nuno

                        ok, iv seen it but i wanted to double check.

                         

                        in this case as i stated all links are conencted in a hub and spoke topology, now the only thing left is which kind of network are they inserted on? So each vpn peer is connected to the datacenter through a Point-to-Point connection network is that right? If so there is no point in running PBR and SLA monitoring to track link downtimes and consequently divert the connections to another link as if one of the point-to-point connections to the datacenter (hub) is down there is no other path to select. correct me if that is not the case.

                         

                        NL

                        • 9. Re: Dynamically changing paths decisions
                          sparky

                          These aren't leased lines / Virtual Circuits .... as stated the connections are mixed, some are fibre most are ADSL,

                          I have my answer now nuno, many thanks

                          • 10. Re: Dynamically changing paths decisions
                            Patrick Geschwindner - CCIE R&S, CCSI

                            I am completely with piperflyer's post. EIGRP has the option to consider LOAD and I don't want to say that it is a bad Idea, BUT you have to use pretty high hysteresis values in this process. It is a great feature but it could easily lead to a slow flapping if the sensitivity is set to high. To adjust this sensitivity you can use the K-values to weight the influence. LOAD based routing should rather be used to steer the addition of less loaded lines to an unequal-path-balancing-bundle to offload traffic from busy links rather then swinging the traffic away from a busy link entirely. Such a construct needs permanent supervision and possibly an adjustment on a regular basis. As I said above, it is a great functionality, but it may also turn into a nasty can of worms if not correctly supervised