October 13th, Cisco 2 notes EIGRP Packet Types The five packet types are: Hello, acknolwedgement, update, query, reply acknowledgement (<-- correct spelling) ----------------------------- The EIGRP Hello Packet - Used to discover, verify, and rediscover neighbor routes - EIGRP routers send hellos at a fixed (and configurable ) interval, called the "hello interval" - The default hello interval dependsd on the badnwdith of thei nterface - Hello interval 5 seconds, hold time 15 seconds for T1 and faster - Hello interval 60 seconds, hold time 180 seconds for slower than T1 - On IP networks, EIGRP hello packets are multicast, 224.0.0.10 - If a niehgbor is not heard from the duration of the "hold time (three times the hello interval)", EIGRP considers that nieghbor down, and DUAL must step in to reevaluate the routing table. If one route is down, you want to remove it from the list of routes (routing table) -- By default, the hold time is three times the hello interval, but an adminstrator can configure both timers as desired. - Unlike OSPF routers, EIGRP routers do NOT need to have the same hello intervals and hold down intervals. You might want to remember the hold time interval and hello interval. What are the hold time and hold time interval? (Er, first one was "hello interval" -- not "hold time") The more routes you have listed, the more worok the router has to do. ----------------------------- Acknowledgement Packet - Acknowledgement packets, which are "data-less" hello packets, are used to ensure reliable communication - Unlike multicast hellos, acknowledgement packets are unicast. - Acknowledgements can be made by piggybacking on other kinds of EIGRP packets, such as reply packets Send a hello? Then the other guy sends an acknowledgement packet. ----------------------------- Update Packet - Update packets are used when a router discovers a new neighbor -- An EIGRP sends unicast update packets to that new neighbor so that it can add to its topology table. -- More than one update packet may be needed to convey all of the topology information to the newly discovered nieghbor - EIGRP updates are only sent when: -- A network is added or removed from the topology ddatabase -- The successor for a given network changes -- THe locally used metric is updated; which is the most effecient route? - The EIGPR router sends a multicast update packet to all niehgbors altering to the change. The moment you see a change in the topology, you're going to tell the other routers what's going on; the people you pass it on to would pass it on to the other routers. Eventually, the entire network would have an idea of what the topology looks like. It's kind of like adding the EIGRP router to the table. To the community. - EIGRP routes exchange routing information the same way as other distance vector routing protocols, but do not send periodic updates. <--- important information How is EIGRP different from distance vector protocols? 1. They do not send periodic updates. 2. They do not send hello packets. What's a successor? It's the path that is initially taken. These are some good CCNA questions. ----------------------------- Query and Reply Packets - EIGRP routers use query packets whenever it needs specific information from one, or all of its nieghbors. -- A reply packet is used to respond to a query. - If an EIGRP router loses its successor and cannot find a feasible successor for a route, DUAL places the route in the "active state" -- The router multicasts a query to all niehgbors, searching for a successor to the destination network. -- Neighbors must send replies that either provide information on successors, or indicate that no successor information is avialable. - Queries can be multicast or unicast, while replies are always unicast. The DUAL algorithm kicks in automatically. It's the grunt worker, the goon. ----------------------------- A rpiter voews ots feason;e siccessprs as meogjnprs tjat are dpwmstrea,. pr c;pser. tp tje destomatopm tjam ot os/ = Of sp,etjomg fgpes wrpmg wotj tje siccesspr. DIA: cma qiocl;y// n;aj n;aj n;aj//// A router views its feasiable suyccesors as niehgbors that are downstream, or closer, to the destination than it is. If something goes wrong with the succesosor, DUAL cna quickly indentify a feasiable succesosr from the topology table, and install a new route to the destination. If no feasiable successors to the destination exist, DUAL places the route in the active state. Entries in the topology table can be in one of two states: active or passive - A passive route is one that is stable and available for use. (It's good; everything is working well; there are no updates or changes) An active route is a route in the process of being recomputed by DUAL. An active route is where you've lost your successor. DUAL has to recompute everything. Recomputation happens if a route becomes unavaiable and DUAL can't find any feasible successors - Another route may exist, it is just that their Reported Distance was greatrer than your Feasible Distance. When does DUAL put it on activee state? What is an active route? What is a passive route? ----------------------------- Configuring EIGRP for IP networks Router (config) #router eigrp autonomous-system-number -- This value must match all routers within the internetwork. Router (config-router)#network network-number - The network command configures only connected networks. Router(config-router)#eigrp log-nieghbor changes -- This command enables the logging of niehgbnors adjacenycy changes to monitor and the stability of the routing system and to help detect problems Router(config-if)#bandwidth kilobits - When configuring serial links using EIGRP it is important to congfigure the bandwidth setting on the interface. If the bandwidth setting is not changed for these interfaces EIGRP assumes the deffault bandwidth on the link instead of the true bnandwidth. ----------------------------- OSPF versus EIGRP OSPF: Supports CIDR and VLSM, rapid convergence, partial updates, niehgbor discovery. EIGRP: Supports CIDR and VLSM, rapid convergence, partial updates, neighbor discovery OSPF: Adminastrator can define route summarization. EIGRP: Automatic route-summarization and user-defined route summarize. Route summarization: finding the common bits and putting them together. OPSPF: Open standard, multivendor support EIGRP: Propriettary; Cisco routers only OSPF: Scalable, adminastrively defined "areas" provid emanageable hierarchy EIGRP: Scalable, but no hierarchical design OSPF: Difficult to implement EIGRP: Easy to implement Think of EIGRP as Cisco-only OSPF: Equal coast load balancing EIGRP: Unequal-coast load balancing What is the difference between OSPF and EIGRP? --------------------------