EIGRP Notes

notes taken to help study for CCIE...used Enabling IP Routing with Cisco Routers by R. Das & K.Chakrabarty, CCIE Routing and Switching by A. Anthony Bruno, Enhanced Interior Gateway Routing Protocol (Cisco Document ID: 16406), Pearson's CCNA Routing and Switching 200-101 Complete Video Course, as well as lots of Internet resources. A lot of this stuff is plagarized from the stated sources, and should be re-worked if ever put into an official publication

EIGRP

Table of Contents

Highlights

Cisco special...
fast convergence
Scalable
Load balancing over unequal cost links
Classless (VLSM support)
Hybrid routing protocol (distance vector that has link-state characteristics)
Multicast - 224.0.0.10
IP protocol 88
classless (VLSM).
Neighbors advertise distance to specific network(s)
Default composite metric of bandwidth and delay
Load and reliability and MTU can be factored into metric
Sends partialroute updates only when changes occur, triggered (onevent), bounded (only send to rtrs that need it)
Support for authentication. MD5. Uses key-chains in config.
By default, equal-cost load balancing; unequal-cost load balancing with the variance command. variance multiplies by successor route and than if other meet feasibility condition successor get’s unequally cost loadbalanced.
Admin distance is

90 for EIGRP internal routes
170 for EIGRP external routes
5 for EIGRP summary routes.
110 OSPF
1 STATIC
120 RIP

Supports split horizon, poison-reverse.
Does auto-summary by default (to most common bit). Sometimes does it wrong. Good idea to disable and do summarization manually.
multicast packets go to 224.0.0.10
uses DUAL (Diffusing Update Algorithm)

Neighbors advertise distance to specific network(s)

Concepts

Protocol-Dependent Modules - Uses different modules to support IP, IPX, Appletalk.

only commonly used protocol that can support even and uneven routes at the same time

Neighbor Discovery and Recovery - Sends/Monitors hello packets. Rtr builds table with EIGRP neighbor info. If hello not received within holdtime, neighbor removed from table.
RTP - uses RTP with sequence numbers to ensure reliable delivery of route updates. Update packets are sent using multicast address 224.0.0.10. Updates are ack'ed using unicast hello packets with no data.
DUAL - (Diffusing Update Algorithm) - developed by Dr. J.J. Garcia Luna-Aceves. Selects best path (successor) and 2nd best path (feasible successor) to reach destination.
Advertised distance is distanced advertised by 1 router to another as the cost to get to a specific network
Feasible distance is the lowest calculated metric of path to reach destination. Distance to EIGRP neightbor plus that neighbor's advertised distance to a specific network
Feasible route - primary path to dest network, based on best feasible distance.
Sucessor route - backup path to dest network, based on feasible distance.
Feasibility Condition - Before route can become Feasible Successor Route, its Advertised Distance (AD) has to be lower than FD (Feasible distance) of Successor Route

EIGRP Metrics

bandwidth (K1 - default)	big
delay (K3 - default)	dogs
reliability (K5)	really
load (K2)	like
mtu	me

Default K values

K1 = 1
K2 = 0
K3 = 1
K4 = 0
K5 = 0

router eigrp 100
  metric weight 0 1 1 1 0 0 (last 5 numbers are K values)
                            (EIGRP neighbors have to have matching K values)

Default Formula -
256*(Bw + Delay)
256 * ( (10,000,000 / min bw in kbs) + (sum of interface delays / 10) )
Full Formula -
K₂*Bw K₅
256*([K₁*Bw + ---------- + K₃*Delay]*[----------------])
(256-Load) (Reliability+K₄)

Values to right of decimals get dropped during calculation.

Stub routers - hub router contains info, performs routing for all networks. Spike routers have only enough info to reach hub router.

Timer Comparison

	Hello	(RIP-Invalid) (OSPF-Suspicious)	Dead (RIP-Flush)	Holddown
RIP	30	180 (6x)	240 (8x)	180
OSPF	10 BMA 30 NBMA	90 (3x)	120 (4x)	5 second delay + 10 seconds Hold
EIGRP	5 60 WAN < 1.544Mbps			15 (3x)
STP	2			20 blocking 15 listening 15 learning forwarding

Packets

EIGRP Opcode	Description
5	Hello	Multicast to 224.0.0.10. Default timer is (5 seconds (60 seconds on WAN links with 1.544Mbps or less)). Holddown timer is 3x hello timer
	Acknowledgment	hello packet with no data. Acks reception of update packet. Sent to unicast address of sender of update packet.
1	Update	contain routing info of destinations. unicast to newly discovered neighbors or multicast to 224.0.0.10 when link or metric changes. Uses RTP.
3	Query	Multicast to find feasible successors to destination.
4	Reply	Sent in response to query packets. Unicast to sender of query in order to provide feasible successor.
6	IPX, SAP

Tables

neighbor table – establish relationship with neighbor
    successor is neighbor that can give you best path to destination
        feasible distance – value of network to successor
        reported distance – router reports FD to next router
        feasible distance = my FD + Reported distance
    feasible successor is next best router that can get to destination based on
    feasibility condition – reported distance has to be less than my own feasible
                distance through successor
   sh ip eigrp neighbors
interface table
Interfaces participating in eigrp AS
sh ip eigrp interfaces
topology table
routes that eigrp knows about
    feasible successor goes in here (not in routing table)
    2 successors – load balancing
    sh ip eigrp topology
    sh ip eigrp topology all-links (will see everything including bad links)
routing table

Type/Length/Value (TLV)

Taken from http://www.rhyshaden.com/eigrp.htm .
There are a number of TLVs, all of them begin with a 16 bit Type field and a 16 bit Length field. There then follows a number of fields that vary depending on the type as given below.

- General TLVs
  - 0x0001 - General EIGRP parameters (applies to any EIGRP packet regardless of protocol)
  - 0x0003 - Sequence (used by Cisco's Reliable Multicast)
  - 0x0004 - EIGRP software version, the original version being 0 and the current version being 1 (used by Cisco's Reliable Multicast)
  - 0x0005 - Next Multicast Sequence (used by Cisco's Reliable Multicast)
- IP TLVs
  - 0x0102 - IP internal routes
  - 0x0103 - IP external routes
- AppleTalk TLVs
  - 0x0202 - AppleTalk internal routes
  - 0x0203 - AppleTalk external routes
  - 0x0204 - AppleTalk cable setup
- IPX TLVs
  - 0x0302 - IPX internal routes
  - 0x0303 - IPX external routes

Commands

router eigrp [as] (AS used to be 2 bytes - 65335, may now be 4
                    bytes (4billion+?))
                    (one AS doesn't play with another unless you
                    resdistribute)
network [ip subnet to participate in routing proc -classful or
        classless if you leave off subnet]
no auto-summary
ip summary-address eigrp AS IP-Addr Mask eigrp stub [receive-only | connected | static | summary]
default network <ip addr or exit interface> (like default gw for router)
redistribute ospf <BW> <D> <R> <L> <M>
    (e.g. redistribute ospf 10000 100 255 1 15000)

show ip eigrp neighbor
show ipv6 eigrp neighbor
show ipv6 eigrp interfaces
show ip eigrp topology
show ipv6 eigrp topology
show ip protocols (gets info about eigrp and other routing protocols) show ipv6 protocols
show ip route
show ipv6 route

(Show's route w/ weights advert fr diff rtr IDs)
    (FD - Feasible Distance - calc'ed distanced connected)
    (RD - Received Distance - Distance recieved from neighbor)
sh ip eigrp topology all-links (will see all incl bad links)
show ip protocols
debug ip eigrp events

IPv4 config

Router One

router eigrp 2000 (The "2000" is the autonomous system - must match on neighboring routers) 
  network 172.16.1.0 0.0.0.255 

  metric weight 0 1 1 1 0 0 (last 5 numbers are K values)
                            (EIGRP neighbors have to have matching K values)

AUTHENTICATION

key chain DEMO
  key 1
  key-string DaKEYstring
int fa 0/1
  ip authentication key-chain eigrp 100 DEMO
  ip authentication mode eigrp 100 md5 (send hash of key string)

Unequal cost routing

Figure variance based on max FD.

FD 1 - 390123
FD 2 - 2304357

variance = roundup(2304357/390123) = 6

router eigrp 100
  variance 6

show ip route (will show unequal cost routes in routing table)

Autosummarization

router eigrp 100
  auto-summary

doesn't work well with discontinguous networks...

Passive interface

listen but don't advertise

router eigrp 100
  passive-interface fa 0/0

show ip protocols (will show passive interfaces)
show ip eigrp neighbors
show ip eigrp interfaces

Router Two

router eigrp 2000
  redistribute eigrp 1000 route-map to-eigrp2000
  network 172.16.1.0 0.0.0.255 
router eigrp 1000 
  redistribute eigrp 2000 route-map to-eigrp1000
  network 10.1.0.0 0.0.255.255
  
route-map to-eigrp1000 deny 10
  match tag 1000
route-map to-eigrp1000 permit 20
  set tag 2000
route-map to-eigrp2000 deny 10
  match tag 2000
route-map to-eigrp2000 permit 20
  set tag 1000

IPv6 config

ipv6 router eigrp 1 (1 is autonomous system)
  router-id 1.1.1.1
int lo0
  ipv6 eigrp 1 (tell interface to participate in as 1)
int fa 0/1
  ipv6 eigrp 1

Troubleshooting

sh ip route (check admin distances and FD)
show ip eigrp topology (FD / advertised distance)
show ip eigrp interfaces
show ip eigrp neighbors
NIT
show ip protocols