Hybrid Routing Protocol
- Rapid convergence (Diffusing Update Algorithm) DUAL
- Stores all available backup routes
- No periodic updates, sends partial updates when path or metric changes
- DUAL sends path updates about a link rather than about the entire route table
- Multi protocol support (appletalk, ipv4, ipv6, IPX)
- Uses multicast and unicast
- Support unequal metric load-balancing
- Supports summarisation anywhere within the network rather than at major network boundaries only
Has three tables: Neighbour Table, Topology Table and Routing Table
Shows the route entries for each destination learned. Best routes are chosen and put into the routing table.
Shows the adjacent eigrp routers
Successor Route = Best Route
Feasible Successor = Backup Route
Advertised distance – metric for an eigrp neighbour to reach a network
Feasible distance – advertised distance for a network learned from a neighbour plus the metric to reach that neighbour.
The router compares all the feasible distances to reach a network and selects the lowest feasible router and puts it into the route table.
Topology databse contains all the routes that are known to each eigrp neighbour.
If a route becomes invalid DUAL checks for a feasible successor to the destination. If none is found then a re computation must occur
EIGRP requires an AS, similar to the process ID for OSPF.
EIGRP automatically summarises on the classful boundary.
EIGRP Load Balancing
EIGRP uses a metric to compute the costs to a given network, by default EIGRP uses two criteria to determine a metric:
You can use the following but they are not recommended because they usually result in frequent recalculation of the topology table:
For IP, IOS load balances across 4 equal-cost paths by default. I can be configured for up to 16 equal-cost paths.
Setting maximum-path to 1 disables load balancing.
Unequal cost load balancing is controlled with the variance command. Values from 1 to 128.
Eg: Variance will determine a feasible successor if the metric is within the variance.
Variance = 2 best path metric = 20 Backup Route = 10, then 10×2 = 20, therefor there is equal cost on both links.
Each key has an ID, the combination of the key ID and the interface associated with the message identifies the MD5 key in use.
Manage Keys Using Key chains
- Troubleshoot Neighbour Relationships
- Troubleshoot Route Table Issues
- Troubleshoot Authentication
Troubleshoot EIGRP Neighbour Relationships
- All Interfaces up/up?
- Getting, not a common subnet error?
- All EIGRP neighbors configured?
- Does Hello info match neighbour?
Both router and neighbour must share a directly connected subnet. EIGRP Hello packets must patch the AS and K values to neighbor up. Debug EIGRP packets to troubleshoot hello information.
Troubleshooting EIGRP Routing Tables
- Advertising all Required Networks
- Route Filters blocking Networks?
- Duplicate EIGRP Router ID’s?
- Is there a discontigious network?
Route table Key:
D = intra-AS Route, D EX = External AS Route
Route ID is formed from the highest IP address assigned to a loopback interface, if no loopback interface, the active interface with the highest IP is used.
Troubleshoot EIGRP Authentication
Use debug eigrp packets to verify authentication information.