Overview:
Enhanced Interior Gateway Routing Protocol (EIGRP) is a Cisco proprietary advanced distance vector dynamic routing protocol.
Study Notes:
- EIGRP uses the Diffusing Update Algorithm (DUAL)
- Fast convergence
- Easy on processor
- Incremental updates
- EIGRP is an Advanced Distance vector protocol
- Combines the best of Distance Vector with Link State protocols, but is considered a Distance Vector protocol (Enhanced)
- Simple to configure
- Flexibility in summarization (not on CCNA, but good to know)
- Unequal cost load balancing
- Doesn’t age out routing entries
- No periodic updates
- 3 tables
- Neighbor table - directly connected to the router
- Topology table - all routes
- Routing table - DUAL algorithm figures out best route
- Uses backup path if one exists in topology table
- Terminology
- Feasible Distance (FD) - to reach the distant network
- Advertise Distance (AD) - how far for neighbor to reach the network
- Successor - primary path
- Feasible Successor - backup path. To be considered a feasible successor, the AD must be less than the FD of the successor
- Active Route - (bad) router is trying to find route to network
- Passive Route - (good) router knows route to network
- Important commands to know
- show ip route - show the routing table
- show ip route eigrp - show only EIGRP routing table entries
- show ip eigrp neighbors - who are the directly connected neighbors
- H = the order in which the neighbor was discovered
- Hold = hold time in seconds waiting for a Hello packet
- Uptime = length of time of neighbor relationship
- SRTT = smooth round-trip timer
- RTO = Retransmission Time Out, time between multicasts basd on SRTT
- Q Cnt = how many messages are in the queue
- Seq Num = sequence number of the last update
- show ip eigrp interfaces - shows all interfaces that EIGRP is enabled on
- show ip eigrp topology - shows all of the FD, AD, Successor, Feasible Successor, etc.
- show ip eigrp traffic - shows number of EIGRP packets sent and received
- show ip protocols - displays a summary of configured routing protocol information
- EIGRP messages are sent via multicast
- HELLO: forms the relationship
- UPDATE: sends updates
- QUERY: asks about routes
- REPLY: response to a query
- ACK: acknowledges UPDATE, QUERY and REPLY messages
- EIGRP uses triggered updates instead of the entire table
- EIGRP is its own layer 4 protocol (protocol number 88). It doesn’t use TCP.
- EIGRP metric - used K values
- K1 - bandwidth (statically configured value). default = 1
- K2 - load (dynamic). default = 0
- K3 - delay (statically configured value; in 10s of microseconds). default = 1
- K4 - reliability (dynamic). default = 0
- K5 - MTU (packet size). default = 0
- EIGRP Metric Calculation (not on CCNA):
256 * [(k1 * bw) + [(k2 * bw) / (256-load)] + k3 * delay)] * [k5 / (reliability + k4)]
- For EIGRP neighbors to form, their k values must be equal
- The CCNA does not cover EIGRP authentication, filtering, manual summarization, redistribution, stub)
- Configuration:
R1#config t
router eigrp 1 (AS number)
network 192.168.0.0 (classful)
no auto-summary (keeps it from summarizing)
Ctrl+Z
R2#config t
router eigrp 1
network 192.168.1.0 0.0.0.3 (wildcard mask)
Ctrl+Z
show ip protocols
show ip route
show ip eigrp topology
show ip eigrp neighbors
show ip eigrp traffic
Labs:
PacketTracer Lab: CCNA-3.11-Configure-verify-and-troubleshoot-EIGRP-for-IPv4.pkt
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