EIGRP – Notes

PACKET TYPES:

• Hello/Ack
  • Neighbor Discovery
  • Multicast advertised on segment, and Unicast responses are returned.
  • Hello with no Data is Ack.
  • Also Keepalive.

• Updates
  • Conveys reachability information for each destination.
  • Sent reliably.

• Queries
  • Sent out to search for another path during convergence.
  • Multicast looking for missing prefix.

• Replies
  • Sent in response to Query, brings prefix from active back to passive (good).
  • Sent reliably.

• Request
  • Used to obtain specific information from neighbor.

Stuck in Active:

• EIGRP router goes into SIA state and removes neighbor adjacency if it does not receive response to query after 3 minutes.
• Continues propagation of query traffic across EIGRP domain.
• Condition where EIGRP router goes active for specific route by sending query, but never receives a reply.

EIGRP Graceful Shutdown

• Enabled by Default
• Neighbor will receive ‘PEER-TERMINATION’ message, implies EIGRP was turned off on interface, do not wait for hold timers.
• Does not work with an interface shutdown. Has to be removal of EIGRP interface or process.

EQUAL COST LOAD BALANCING:

• Multiple paths in RIB for same destination prefix – ECMP

UNEQUAL COST LOAD BALANCING:

• Installation of both successor routes and feasible successors into the EIGRP RIB.
• Variance value can be modified to enable this feature. Variance value is the FD (best available route metric – successor) multiplied by the variance multiplier.
  • Any feasible successor’s FD with metric below EIGRP variance value is installed into RIB.
  • Feasible Successor needs FD to be less than successor route multiplied by variance value.

EIGRP Stub Routing:

• Stub router will advertise all connected and summary routes to upstream EIGRP speakers (Default).
• Stub router never gets queried by upstream EIGRP speakers for route information.
• Helps with using branch as traversal for link failure.
• Branch(config-router)#eigrp stub (default advertise connected and summary)

EIGRP Finite State Machine:

• All the states and processes that DUAL uses to compute metrics and routes.
• Passive route states equate to a stable network and no re-computation being needed by DUAL.
• Active route states equate to DUAL re-computing metrics and/or locations for routes.
  • No feasible successor begins query to EIGRP neighbors.

EIGRP Add Path:

• DMVPN Feature
• Allows for load balancing traffic between two spokes over EIGRP.
• By default a hub will not advertise more than one route to a spoke destination, even if the hub has two equal cost paths. If a spoke lost a primary route EIGRP would have to reconverge.
• Configure:
  • HubRouter(config)#router eigrp NAMEMODE
  • HubRouter(config-router)#address-family ipv4 unicast autonomous-system 1
  • HubRouter(config-router-af)#af-interface tunnel1
  • HubRouter(config-router–af-interface)#add-paths <number of paths>

EIGRP LOOP FREE ALTERNATE FAST REROUTE

• Allows for taking a backup path in the network within 50ms
• Installs both the Successor and Feasible Successor in the routing table, not just successor. Lowers failover time.
• Interior Gateway Protocols calculate LFAs using 2 methods:
  • Per-Link:
    • Found in multiaccess segments.
    • All links use the same next hop address.
    • Single secondary backup link.
    • Less CPU and simple to calculate.
  • Per-Prefix
    • Calculates LFA for each destination.
    • Enforces FRR or failover uses two different backup routes or next hops.

• If there are multiple LFAs then FRR needs to choose one. List of tie breakers below, lower metric wins:
  • Interface Disjoint
    • Do not choose an LFA that goes out the same interface – 20
  • Linecard Disjoint
    • Do not select LFA that exits out same line card – 40
  • Lowest Repair Path Metric
    • Choose LFA with lowest metric – 30
  • Shared risk Link Group (SRLG)
    • Prefer LFA not sharing the same Share Link Group

EIGRP Summary Leak Map

• Advertises more specific route(s) on interface in addition to summary.
  • 1 – Create access list
    • R1(config)#ip access-list standard Leak
    • R1(config-std-nacl)#permit 10.30.1.0 0.0.0.255
  • 2 – Create Route Map referencing access list
    • R1(config)#route-map Leak-Example 10
    • R1(config)#match ip address Leak
  • 3 – Use summary command under interface
    • R1(config)#interface Gig0/2
    • R1(config-if)#ip summary-address eigrp 1 10.30.0.0/16 leak-map Leak-Example
• In the routing table of neighbor there is now a summary address (10.30.0.0/16) and a longer prefix route of 10.30.1.0/24

EIGRP Stub

• Typical EIGRP configuration for branch routers.
• Way to stop queries from being sent to a router when there are topology changes or links going down.
• Types of EIGRP Stub networks:
  • Redistribute – Stub router can advertise redistributed routes.
  • Summary – Stub router can advertise summary routes.
  • Connected – Stub router can advertise directly connected.
  • Static – Stub router can advertise redistributed static routes.
  • Receive-only – Stub router does not advertise any networks, only receives.
• Default ‘eigrp stub’ command uses connected and summary.

EIGRP Stub Leak-Map

• Similar to EIGRP Summary leak map, allows router to be configured as stub but still have exceptions for routes being advertised.
• R1(config)#router eigrp 1
• R1(config-router)#eigrp stub leak-map <name of created route-map>