EIGRP – unequal cost load balancing, support for networks 255 hhops away, rapid convergence

DUAL – diffusing update algorithm to identify paths

Router can run multiple EIGRP processes separated by AS number. Autonomous System

PDM – protocol dependent modules to support multiple network protocols

– successor route – route w/lowest path metric
– successor – first next hop router for successor route
– feasible distance – metric value for lowest metric path to reach destination
– reported distance – distance reported by router ot reach prefix
– feasibility condition – for route to be considered a backup route
– feasibility successor – a route that satisfies feasibility condition maintained as backup route

Topology Table
– network prefix
– EIGRP neighbors that advertise prefix
– metrics from each neighbor
– values used for calculating metric

EIGRP Packet Types
– Hello
– Request
– Update
– Query
– Reply

RTP – reliable transport protocol ensure packets are delivered

EIGRP forms neighbors
– Requires neighbor relationship before routes are processed and added to RIB

Matches Required for Neighborship
– metric formula K values
– primary subnet
– AS number match
– authentication

2 Methods Classic and Named
Classic – most config in process, some under interface
Named – hierarchy – address family, interface, topology,

passive interface – enabled w/routing protocol to advertise its interface into RIB but does not establish neighborship with other routers associated w/interface

authentication – authenticated routers become eigrp neighbors encrypt with md5 authentication w/keychain key # and password

wide metric – advertising and identifying interface speeds and delay accounts for higher metrics

load balancing – allows multiple successors to be installed into rib

unequal cost load balancing must change variance multiplier

variance value – fd for a route multiplied by eigrp variance multiplier

failure detection
– default timers 5 sec, 60 on slow
– hold timers 15 sec, 180 on slow

stuck in active
– if router receives no response within 90 sec

summerization – reducing routing table by advertising less specific network prefix than multiple more specific network prefixes

summary discard routes – routing loop prevention

summerization metrics – lowest metric of component routes

stub router – advertise all other neighbors isolated should not be queried when routes go active

stub site router – advertises to all other upstream neighbors that are isolated

eigrp max available bandwidth 50% and 50% for data

split horizon – prevents advertisements of reverse routes enabled by default

offset list – modify metric value of route

Neighborship Might Not Form If…
– int down
– mismatched as numbers
– incorrect network statement
– mismatched K value
– passive interface
– different subnets
– authentication
– Timers

ACL may be denying EIGRP multicast address


FF02::A mutlicast link local
classic and named
router id
on interface
no concept of classless/classfull
default route ::/0

DHCP, DHCPv6, IP Routing

Discover – broadcast messages
Offer – server responds with this
Request – client responds with request to use what’s offered
Ack – serrver acknowledges that it is leased

ip helper – address to configure router to replay dhcp messages to server
service dhcp
interface _______
ip helper-address x.x.x.x

ip dhcp excluded – address x.x.x.x x.x.x.x
prevents DHCP from assigning those ip address

ip dhcp pool POOL-A
creates pool which hands out ip addresses in POOL-A

169 ip address means problem
APIPA – IPv4 address when server unavailable possibly a layer 2 issue /16


neighbor discovery – IPv6 protocol for address auto config, duplicate addresses, detection, router, neighbor, prefix discovery, neighbor address resolution, parameter discovery

EUI-64 – 1st half of mac address, 7th bit flipped, FFFE, last half of mac address

SLAAC – enables device to configure its own IPv6 address and default gateway without DHCPv6 server
Cisco Routers enable manually on interface

IPv6 address autoconfig

Router Solicitation – messages to determine whether there are any routes connected to local link then wait for

Router Advertisement – to identify prefix used by router (default gateway)

Stateless DHCPv6

Routers RA – used by clients to automatically determine IPv6 address

DHCPv6 Operation
Solicit – sends FF02 which is all DHCPv6 multicast addresss
Advertise – server responds with unicast messages to offer ip address info
Request – client sends this confirming address provided and parameters
Reply – server finalized w/this message

DHCPv6 Relay Agents – relays solicit messages to DHCPv6 server in different IPv6 network

Packet Forwarding – forwarding packets through router, ip routing

Layer 3 to Layer 2 mapping found in arp cache

ARP – used on ethernet lan by devices to determine layer 2 mac of known layer 3 ip address

FIB contians layer 3 info similar to ip routing table

Adjacency table contains frame header info required by router used by CEF stores layer 3 addressing for all FIB entrires

CEF – cleans info from routing table and layer 3 to layer 2 mappsings

control plain – protocols between routers

data plane – process forwards packets through multilayer switch

AD – used to maniupulate path selection

Static route – manualy configured by admin using ip route or IPV6 route command

proxy arp – allows router to respond to ARP requests with its own mac address if it has route in routing table to ip address in arp request