Lab 4 Dynamic RoutingAnnouncementsRoutingSlide 4Routing Information Protocol(RIP)RIP-Lab4: ImplementationRIP-Lab4RIP-Lab4: RIP Packet FormatSlide 9RIP-Lab4: Periodic UpdatesRIP-Lab4: Route TimeoutsRIP-Lab4: Routing LoopsSlide 13RIP-Lab4: CodeSlide 15RIP-Lab4: Running the LabSlide 17Lab 4Dynamic RoutingCS144 Review Session 5October 30, 2009Samir SelmanAnnouncements•Lab 4 : Due in 2 weeks (Thurs ,Nov 12)•Lab 3 : Due Yesterday•For those of you submitting late, contact us before your deadline if you need an additional extension. Tell us:–Where you are–How much more time you needRouting•Static Routing (Implemented Lab 3)•Dynamic Routing:–Unicast Routing:•Interior Gateway Protocols (RIP, OSPF, IS-IS)•Exterior Gateway Protocols (BGP)–Multicast Routing•Examples: Multicast OSPF (MOSPF) , Multicast BGP(MBGP)•This Lab will cover RIPRoutingRouting Information Protocol(RIP)•RIP:–Routing Protocol based on Bellman-Ford, Distance Vector algorithm.–Intra-domain routing algorithm or interior gateway protocol (IGP)–Cost is usually hop count–Limitations:•The protocol is limited to networks whose longest path is 15 hops•The protocol depends upon "counting to infinity" to resolve certain unusual situations•The protocol uses fixed "metrics" to compare alternative routesRIP-Lab4: Implementation•Lab 4 is just a subset of RIP•Want you to focus on the RIP part of the router => Supplied you with ‘dr’ binary•Binary relies on API implemented in a shared library to handle dynamic routing. You should implement this library.•Write code in dr_api.h and dr_api.cRIP-Lab4•Each Router has a forwarding table containing an entry for every destination network.•Forwarding table Entry: (Dest Network, Cost, Next-hop, Time Stamp).–Dest Network: Represented by a network address and a network mask (X.X.X.X / Y)–Cost: Sum of link costs to reach destination.–Next-hop: IPv4 address of next router along the path to destination–Time Stamp: Used to timeout routing entriesRIP-Lab4: RIP Packet Format•RIP packet:•Command: Indicates whether packet is request or response–Request: Asks that a router sends all or part of its routing table. (For this Lab you don’t need to worry about RIP Requests)–Response: Either unsolicited routing update or a response to request.•Version: RIP version used. Lab 4 uses RIP V2•AFI: Address family used. (AF_INET)•Route Tag: Not used in this lab (replaced by pad)RIP-Lab4: RIP Packet Format•RIP packet:•Network address: IP address for the entry•Subnet Mask: Contains subnet mask for the entry•Next Hop: Indicates IP address of the next hop to which packets for the entry is forwarded.•Metric: Indicates how many hops(routers) have been traversed in the trip to the destination. (16=unreachable)RIP-Lab4: Periodic Updates•Send routing updates:–At regular intervals (periodic)–When a router changes the metric to a route (Triggered Updates)•Every 10 sec send RIP reply message to all neighbors containing complete routing table•Triggered update when an interface goes down or cost of a local interface changes.RIP-Lab4: Route Timeouts•Dynamic Route:–Route learned from a neighboring router–Have a Timestamp field per entry–When receive an update, a router sets the entry Timestamp value to the current time.–Periodically check if entries expired (current time – updatetime > 20 sec.–If an entry expires => set the Cost = INFINITY•Local Route:–Directly Connected Networks–Invalid TTL= -1–Next_hop_ip = 0RIP-Lab4: Routing Loops•Split Horizon with Poisoned Reverse–Prevent a loop from occurring between two nodes–Advertise information back to source with cost INFINITY.–What about loops with more than 2 nodes. eq: A -> B, B -> C, C -> A ?•Cannot stop such a loop using split horizon.•This loop will only be resolved when the metric reaches infinity and the network involved is then declared unreachable•Speed up process using triggered update.RIP-Lab4: Routing LoopsRIP-Lab4: Code•You should only touch the safe_ methods (threading handled already for you)•Routing table entry/** a single entry in the routing table */typedef struct route_t { uint32_t subnet; /* destination subnet which this route is for */ uint32_t mask; /* mask associated with this route */ uint32_t next_hop_ip; /* next hop on on this route */ uint32_t outgoing_intf; /* interface to use to send packets on this route */ uint32_t cost; struct timeval last_updated; int is_garbage; /* boolean which notes whether this entry is garbage */ route_t* next; /* pointer to the next route in a linked-list */} route_t;RIP-Lab4: Code•safe_dr_get_next_hop(ip): Called when router needs to know how to route a packet. Returns which interface packet should be sent out and IP address of next hop. •safe_dr_handle_packet: Method called when router receives a dynamic routing packet.•safe_dr_handle_periodic(): Method called periodically by the router.•safe_dr_interface_changed: When interface goes up or down or upon a change in direct link cost •dr_init: Used to initialize any internal data structures.RIP-Lab4: Running the Lab•First start the lvns server–./lvns -t simple.topo•If the server is running on the same machine as the dr instance, then you can start a router which takes control of a node named "dr1" like this: –./dr -v dr1•If you are running dr from a separate location you'll want to specify the server‘s address and port explicitly: –./dr -v dr1 -s myth5.stanford.edu -p
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