EIGRP

RD, CD, S, FC, FS, FD (DA#1)

Reported Distance (aka advertised distance) A router's best path, which it will advertise to other neighbors
Compouted Distance My distance through neighbor(s) to a network
Successor The lowest CD path routing table
Feasibility Condition A routers reported distance must be lower than my best path to be considered
Feasible successor Any other paths that meet the feasibility condition, topology table
Feasible distance Initially equal to distance of successor - lowest value in history of link, used for loop avoidance. Can cause DUAL algorithm to run again, vs trying to converge on a looped path

EIGPR classic metric calulation Delay + Bandwidth * 256

via (CD / RD),

Show S and FS

R1#show ip eigrp topology | beg 10.1.1.0
P 10.1.1.0/24, 1 successors, FD is 2560
        via 12.1.1.2 (2560/256), GigabitEthernet0/2
        via 13.1.1.3 (5120/1280), GigabitEthernet0/3

Show all routes, even those that do not meet the FC

R1#show ip eigrp topology all-links | beg 10.1.1.0
P 10.1.1.0/24, 1 successors, FD is 2560, serno 4
        via 12.1.1.2 (2560/256), GigabitEthernet0/2
        via 14.1.1.4 (4096/3072), GigabitEthernet0/4 ! Not shown becasue RD > CD of best path
        via 13.1.1.3 (5120/1280), GigabitEthernet0/3

Finding ASN (DA#2)

Neighbor Adj doesn't come up? Either ASN mismatch, or neighbor is unicasting and I am multicasting 1. Try a neighbor command to unicast 2. Try to find ASN using debug command

access-list 100 per eigrp host <neighbor-ip> host 224.0.0.10
debug ip packet detail 100 dump

*Nov 19 18:04:06.744: IP: s=56.1.1.5 (GigabitEthernet0/5), d=224.0.0.10, len 60, rcvd 0, proto=88
08E1D1C0:                       0100 5E00000A            ..^...
08E1D1D0: 50000001 00060800 45C0003C 00720000  P.......E@.<.r..
08E1D1E0: 01589F28 38010105 E000000A 0205E66E  .X.(8...`.....fn
08E1D1F0: 00000000 00000000 00000000 00000064  ...............d
08E1D200: 0001000C 01000000 0000000F 00040008  ................
08E1D210: 14000200

undebug all

Find ASN

Look for E000000A, this is 224.0.0.10 in hex
Go 5 blocks after that block 00000064 this is ASN in hex
64 hex to decimal = 100
ASN is 100

Find K values

Look at 7th block 01000000, and first two digits in 8th block 00
K1 = 01, K2 = 00, K3 = 00, K4 = 00, K5 = 00

metric weight 0 1 0 0 0 0 (ToS, K1, K2, K3, K4, K5)

Summarization (DA#3)

Unsummarized routes with different delays

R2#show ip route eigrp | beg Ga
Gateway of last resort is not set

      1.0.0.0/24 is subnetted, 4 subnets
D        1.1.0.0 [90/3072] via 12.1.1.1, 00:01:38, GigabitEthernet0/1
D        1.1.1.0 [90/28416] via 12.1.1.1, 00:01:38, GigabitEthernet0/1
D        1.1.2.0 [90/54016] via 12.1.1.1, 00:01:38, GigabitEthernet0/1
D        1.1.3.0 [90/79616] via 12.1.1.1, 00:01:38, GigabitEthernet0/1

After summarization

R2#show ip route eigrp | beg Ga
Gateway of last resort is not set

      1.0.0.0/22 is subnetted, 1 subnets
D        1.1.0.0 [90/3072] via 12.1.1.1, 00:00:07, GigabitEthernet0/1

Note cost of a summary is based on the lowest cost of a specific route within the summary.

Leaking routes

Just use a more specific ip summary-address

Use a leak map

ip summary-address eigrp 100 <subnet> <mask> leak-map <route-map-name>

route-map tst permit 10
 match ip address 1

access-list 1 permit <subnet> <inverse-mask>

Leak map refs non-existant route-map? Only summary advertised
Leak map refs route-map that doesn't have an ACL? Summary + specific routes advertised
Leak map refs route-map that refs ACL that doesn't exist? Summary + specific routes advertised

Default Routes

Options for injecting default route in EIGRP?

(best?) ip summary-address eigrp <asn> 0.0.0.0 0.0.0.0
- Allows 'per neighbor' default route injection
- Will surpress all specific routes
ip route 0.0.0.0 0.0.0.0 Null0, then network 0.0.0.0 in EIGRP
- Works because Null0 becomes a directly connected interface in routing table
- Will not suppress other specific routes
ip route 0.0.0.0 0.0.0.0 <next-hop>, then redistribute static in EIGRP
- Will not suppress other specific routes
- Default route will have AD of 170, external route
ip default-network <network>, then redistribute static in EIGRP
- If subnetted IP is used, static route for network will be injected
- Cisco says being removed soon (classfull command)

Authentication

Classic Mode - supports MD5
- Keychain based authentication

key chain <keychain-name>
 key 1
  key-string <password>

interface <intf>
 ip authentication key-chain eigrp <asn> tst
 ip authentication mode eigrp <asn> md5

See password in double quotes show key-chain <keychain-name>

Named Mode - supports MD5 or SHA-256

MD5

key chain <keychain-name>
 key 1
  key-string <password>

router eigrp <name>
 address-family ipv4 as <asn>
  af-interface <intf | default>
   authentication mode md5
   authentication key-chain <keychain-name>

SHA-256 does not use key chain

router eigrp <name>
 address-family ipv4 as <asn>
  af-interface <intf | default>
   authentication mode hmac-sha-256 <password>

Metric Calculation (DA#4)

Before composite metric is calculated, vector metric is calulated
- Vector metric "worst case scenerio"
  - Advertised to neighbors
  - Bandwidth = worst bandwidth along the path
  - Delay = sum of delay along the path

K values

Default, K1 and K3 = 1, others = 0 - K1 = bandwidth - K2 = load - K3 = delay - K4 = reliability - K5 = MTU

Classic Mode metric calculation

[(K1 x BW) + (K2 x BW 256-load) + (K3 x DLY)] x [K5/K4 + reliability] x 256

Bandwidth = Slowest BW / 10,000,000 Delay = Sum of Delays / 10

So by default: (BW + DLY) x 256

Named Mode metric calculation

When is wide metric in use?

EIGRP version 9 or above

show eigrp tech-support
eigrp-release      :  20.00.00 : Portable EIGRP Release

Metric version 64bit = wide metric

R8#show eigrp protocols | inc rib-scale|version
Metric rib-scale 128
Metric version 64bit

Composite metric - 64 bits long
Rib-scale - routing table can only hold 32 bit number, so metric gets divided by rib-scale
- Need to change on all routers on same AS If you don't, it won't cause loop, but will cause suboptimal routing

FD is 13189120, RIB is 103040 13189120 / rib-scale (128) = 103040

R7#show ip ei topology 8.8.8.0/24
...
State is Passive, Query origin flag is 1, 1 Successor(s), FD is 13189120, RIB is 103040
Descriptor Blocks:
78.1.1.8 (GigabitEthernet0/8), from 78.1.1.8, Send flag is 0x0
    Composite metric is (13189120/163840), route is Internal
    Vector metric:
        Minimum bandwidth is 100000 Kbit
        Total delay is 101250000 picoseconds
        ...

Nonchangable values from EIGRP spec
- EIGRP_BW = 10,000,000 (10 million)
- EIGRP_DLY = 1,000,000 (1 million)
- Multiplier = 65536

Metric calculation
- wide metric = throughput + latency
    - throughput = (EIGRP_BW x Multiplier) / Minimum bandwidth
    - latency = (Total delay x Multiplier) / EIGRP_DLY

Advanced Tagging (DA#5)

Using dotted decimal notation with tagging

(config)#route-tag notation dotted-decimal

Filter for odd tagged routes using DDN route tags

route-tag list RT seq 5 permit 0.0.0.1 0.0.0.254

route-map tst permit 10
 match tag list RT

router eigrp <name>
 !
 address-family ipv4 unicast autonomous-system <asn>
  !
  topology base
   distribute-list route-map tst in

Filter for an odd number on 4th octet in an ACL

This demonstrates same thing using an ACL that you can do with route tag.

`access-list 1 permit 1.1.1.1 0.0.0.254`
- Matches 1.1.1.1/32, 1.1.1.3/32, etc.
- Works due to "AND-ing" process (binary)

1.1.1.1/32 match

Last octet .1 = 0000 0001
Wildcard .254 = 0000 0001
AND             _________
                0000 0001

1.1.1.1/32 no match

Last octet .2 = 0000 0010
Wildcard .254 = 0000 0001
AND             _________
                0000 0000

1.1.1.5/32 match

Last octet .5 = 0000 0101
Wildcard .254 = 0000 0001
AND             _________
                0000 0001

Stub Routing

When a path is lost, EIGRP takes active role to find new path.
EIGRP sends QUERY to ask neighbors.
- QUERY gets propogated downstream until someone answers
- Neighbors must respond within 3 mins
  - No response? Path is SIA (stuck in active) until reply recieved

Stub router

Sets stub flag, QUERY is never sent to stub router

Only advertise a specific type of routes

router eigrp <asn>
 eigrp stub (connected | summary | static | redistributed | receive-only)

Leak some routes through a stub?

router eigrp <asn>
 eigrp stub connected summary leak-map <map>

Leak specific routes to specific neighbors?

route-map <tst> permit 10
 match ip address 2
 match interface Gi0/2
route-map <tst> permit 20
 match ip address 3
 match interface Gi0/3
route-map <tst> permit 90

ADD_PATH (DA#6)

Can advertise multiple paths to the same network, so that there is no wait for convergence.

router eigrp <name>
 address-family ipv4 as <asn>
  af-interface <intf>
   add-paths 2

FRR LFA (DA#7)

"BFD on Demand"

Requires named mode
Creates a BFD session

Configuration:

router eigrp <name>
 address-family ipv4 as <asn>
 topology base
  fast-reroute ...

FRR options:

R9(config-router-af-topology)#fast-reroute ?
  load-sharing  Distributes repair paths equally among links and prefixes
  per-prefix    Enable Fast-Reroute Per-Prefix
  tie-break     Set repair path preference

When using per-prefix:

R9#show ip route 11.1.1.1 | inc Repair
      Repair Path: 10.9.12.12, via GigabitEthernet12

R9#show ip cef 11.1.1.1
11.1.1.1/32
  nexthop 10.9.10.10 GigabitEthernet10
    repair: attached-nexthop 10.9.12.12 GigabitEthernet12

per-prefix calculate repair path on a per prefix basis
load-sharing treat the paths as equal
tie-break example: interface-disjoint, chose a repair path on a different interface for redundancy purposes

R9(config-router-af-topology)#fast-reroute tie-break ?
  interface-disjoint         Prefer Interface disjoint repair path
  linecard-disjoint          Prefer line card disjoint repair path
  lowest-backup-path-metric  Prefer repair path with lowest total metric
  srlg-disjoint              Prefer SRLG disjoint repair path

Order of priority to select repair path SRLG (prio 10), Interface (prio 20), Lowest metric (prio 30), line card (prio 40)

SRLG - Shared risk link group

interface <intf>
 srlg gid <gid>

EIGRP Filtering (DA #10)

Filter using maximum-hops

router eigrp <asn>
 metric maximum-hops <max-hops>

Filter by setting AD

! Identify network
access-list 1 permit 2.0.0.0 0.255.255.255

! Set admin distance to 255 when advertised by router 100.1.1.3
router eigrp 100
 distance 255 <neighbor-ip> <neigh-wildcard> <acl>
 ! distance 255 100.1.1.3 0.0.0.0 1

Using distribute-list

! Identify network
access-list 1 deny 4.0.0.0 0.255.255.255
access-list 1 permit any

router eigrp 100
 distribute-list 1 in Gi0/2
 ! distribute-list <acl> <direction> <intf>

Using extended ACL

! 100.1.1.2 = Advertising router
! 3.0.0.0/8 = Network to be filtered
access-list 100 deny ip host 100.1.1.2 3.0.0.0 0.255.255.255
access-list 100 per ip any any

router eigrp 100
 distribute-list 100 in Gi0/0

Filter by metric range Example - filter metrics between 7936-10496

Calculate a deviation 7936 + 10496 = 18432 / 2 = 9216 (middle of range) 10496 - 7936 = 2560 / 2 = 1280 (deviation from middle of range)

Route map says "If route metric is within range of 9216 +- 1280, deny"

route-map tst deny 10
 match metric 9216 +- 1280
route-map tst permit 20

router eigrp 100
 distribute-list route-map tst in

Filter by internal/external route ``` router eigrp 100 distance eigrp 90 255 ! distance eigrp