INE R&S ATC053 ~ ATC067 - EIGRP

053 - EIGRP Overview
054 - EIGRP Auto-Summary
055 - EIGRP Split-Horizon
056 - EIGRP Update Types, EIGRP Neighbor, EIGRP Passive-Interface
057 - EIGRP Hello-Interval, EIGRP Hold-Time
058 - EIGRP Authentication
059 - EIGRP Time Based Authentication
060 - EIGRP Path Selection, EIGRP Metric Weights, EIGRP Traffic Engineering
061 - EIGRP Unequal Cost Load Balancing, EIGRP Variance
062 - EIGRP QUERY, EIGRP Summarization, EIGRP Leak-Map
063 - EIGRP Stub Router Advertisement
064 - EIGRP Default Routing
065 - EIGRP Route Filtering
066 - EIGRP Router-ID
067 - Miscellaneous EIGRP Features

EIGRP Overview

• Hybrid IGP
  – Properties of both link-state and distance vector
    • Forms active adjacencies but still uses split-horizon
    • DUAL guaranteed loop free but still “routing by rumor”
• Uses its own transport protocol
  – IP protocol 88
  – Multicast to 224.0.0.10 to establish adjacencies
  – Unicast and multicast to synchronize the topology

Enabling EIGRP

• Enable the global process
  – router eigrp[AS]
  – AS number must match to be adjacent
• Enable the interface process
  – network [address] [wildcard]
  – Similar to OSPF network statement
 
Verifying EIGRP

• Verify EIGRP is enabled
  – show ip eigrp interfaces [detail]
  – show ip protocols
• Verify EIGRP transport
  – debug eigrp packet [hello | ack| update | query | reply | …]
• Verify neighbor adjacencies
  – show ip eigrp neighbors [detail]
  – Queue count should be 0 if converged
• Verify EIGRP topology
  – show ip eigrp topology[all-links]
  – show ip eigrp topology [prefix/len]

EIGRP Auto-Summary

• LikeRIPv2, EIGRPis classless but does automatic classful summarization by default
– Disabled with no auto-summary under process
• VLSM is supported within the same major network
• Advertisements between major network boundaries are summarized to classful boundary
– Will not result in traffic black hole due to discard route

EIGRP Split-Horizon

• Always on
– Undesired in partial mesh NBMA
• Disabled at interface level
– no ip split-horizon eigrp[AS]
• Won’t cause a loop due to DUAL feasibility condition

EIGRP Update Types

• EIGRP uses multicast and unicast
– HELLO, QUERY, UPDATE, etc. multicast to 224.0.0.10
– UPDATE, ACK, REPLY, etc. unicast to neighbor
• neighbor statement disables multicasts
– Implies that all neighbors must agree
• passive-interface stops both unicast and multicast hellos
– Implies no adjacencies on passive links

EIGRP Timers

• Hello interval
– How often I send hellos on a link
– ip hello-interval eigrp[AS] [seconds]
• Hold time
– How long you should wait to declare me down
• Opposite of OSPF hello & dead interval
– ip hold-time eigrp[AS] [seconds]
• Timers don’t have to match for adjacency to form

EIGRP Authentication

• Supports MD5 authentication only
• Uses key chains like RIPv2
– Whitespace counts as a character
– Key number must match
– Supports automatickey rotation
• Applied at interface level
– ip authentication mode eigrp[AS] md5
– ip authentication key-chain eigrp[AS] [key-chain]

EIGRP Time Based Authentication

• Key chain supports multiple key numbers
  – Router always sends lowest valid key
• Key number’s validity is based on time
  – accept-lifetime
    • When is key valid to be received
  – send-lifetime
    • When is key valid to be sent
• Automatic rotation by defining different validity times
  – Implies time must be agreed upon
  – accept-lifetimeshould overlap in case of mismatch of time

EIGRP Path Selection

• EIGRP chooses path with lowest composite metric based on
– Bandwidth
  • Inverse lowest bandwidth along path in Kbps scaled by 10^7 * 256
– Delay
  – Cumulative delay along path in tens of microseconds (μs) scaled by 256
– Load
  • Highest load along path
– Reliability
  • Lowest reliability along path

EIGRP Metric Calculation

• Composite metric is computed as…
  – metric = [k1 * bandwidth + (k2 * bandwidth)/(256 -load) + k3 * delay]
  – If k5 != 0, metric = metric * [k5/(reliability + k4)]
• Route with lowestmetric is the “Successor”
• Successor’s metric is the “Feasible Distance” (FD)

EIGRP Metric Weighting

• “K” values allow for manual administrative weighting
  – Default K values are K1 = 1, K2 = 0, K3 = 1, K4 = 0, K5 = 0
  – Implies default composite is bandwidth + delay
• Can be modifiedwith metric weights command
  – Must match for adjacency to occur

DUAL Terms in Detail

• Successor –Best path to a destination
• Feasible Distance (FD) –Composite metric of best path
• Feasible Successor (FS) –Backup path to a destination
• Advertised Distance (AD) –Composite metric learned from neighbor
• Local Distance (LD) –Composite metric to reach local neighbor
• Feasibility Condition (FC) –Criteria for valid backup paths

DUAL Path Selection in Detail

• Each update includes the metric the upstream router uses to reach destination (AD)
• Local router knows the metric to reach each upstream router (LD)
• Best path (successor) is chosen based on lowest AD + LD

Feasibility Condition in Detail

• Once best path is chosen, additional paths are examined for backup routes
• Feasibility Condition (FC) finds loop-free backup routes via logic…
  – If AD < FD, path is loop-free and viable backup
  – e.g. if your metric is lower than mine, you are closer to the destination and loop-free
• Paths that meet the FC are Feasible Successors (FS)
  – Only Feasible Successors can be used for unequal cost load balancing

EIGRP Traffic Engineering

• Bandwidth is lowest bandwidth along the path on a per prefix basis
  – Essentially the bandwidth bottleneck
  – Hard to predict what a modification will affect
• Delay is cumulative on a hop-by-hop basis
  – Easier to influence path selection with
  – delay interface command

EIGRP Unequal Cost Load Balancing

• EIGRP allows load distribution among unequal paths
  – Controlled by variance command
• If feasible distance * variance > feasible successor, load balancing occurs
  – Only feasible successors are candidate for load balancing
• Automatically calculated traffic share count causes links to be used in ratio proportional to their composite metrics
  – Actual load balancing still controlled by switching path

EIGRP Scalability

• EIGRP can achieve sub-second reconvergence through use of backup routes
  – Backup routes are Feasible Successors if they pass the Feasibility Condition
• If no backup routes QUERY message is sent
  – Asks other neighbors for an alternate path
• QUERY domain can be bounded by
  – Summarization
  – Stub router advertisement

EIGRP Summarization

• ip summary-address eigrp[network] [mask] [AD] at the link level
• Features
  – Supports any bit boundary including 0.0.0.0/0
  – Automatically suppresses subnet advertisements
    • Can advertise subnets through leak-mapargument
  – Administrative Distance defaults to 5
    • Allows for floating summaries
  – Automatically generatesdiscard route
    • Can be removed with AD of 255

EIGRP Stub Router Advertisement

• Reduces size of EIGRPQUERY domain
  – Stub routers don’t receive QUERYmessages
• Processlevel eigrpstub [args]
  – Arguments controls what router advertises
  – Defaults to connected routes and summary routes

EIGRP Default Routing

• EIGRP supports default routing two ways
  – Candidate default network
    • ip default-network [network]
  – Native advertisement of 0.0.0.0/0 prefix
• default-information command in EIGRP does not behave the same as other protocols

IP Default-Network

• Candidate default network is backwards compatible with IGRP
  – IGRP didn’t support native 0.0.0.0/0 advertisement
• Default network must be…
  – Dynamically learned through EIGRP
  – Not directly connected
  – Classful network
• Limited application due to these restrictions

Native Default Advertisement

• Native 0.0.0.0/0 network can be advertised via…
  – Static default route to an interface + network 0.0.0.0 under EIGRP process
  – Redistribution from static or another protocol
  – Summarization

EIGRP Inbound Route Filtering

• Distribute-list
  – Standard access-list
  – Extended access-list
    • Source is route source, destination is prefix
  – Prefix-list
• Offset-list
• Distance
  – 255 = infinite
  – Can be per prefix and per neighbor
• Route-map
  – Metric filter
  – Route tag filter

EIGRP Outbound Route Filtering

• Distribute-list
  – Access-list
  – Prefix-list
• Offset-list
• Passive-interface
• Route-map
  – Metric filter
  – Route tag filter

EIGRP Router-ID

• Used for external loop prevention
  – Don’t acceptself originated external routes
  – Duplicate router-ids can result in traffic black holes
• Can be manually specified with eigrp router-id [address]under process

MiscellaneousEIGRP Features

• Next-hop-self
• Maximum prefix
• Bandwidth pacing
• Default metric
• Neighbor logging
• Metric holddown
• Maximumhops
• Know the command reference
  – Little functionality as compared to OSPF