EIGRP Flashcards
What IP protocol number and multicast address is used by EIGRP
IP 88
Multicast address 224.0.0.10
What are the 2 ADs given to EIGRP routes
90 for internal routes
170 for externally learned routes
List the 5 packet types used to EIGRP for neighbor communication
Hellos Updates Acknowledgements Queries Reply’s
What mechanism does EIGRP use to ensure reliable delivery of packets
RTP - reliable transport protocol
What is the default hello and hold time for EIGRP
Hello - 5 seconds
Hold - 15 seconds
What Information is carried in an EIGRP ‘Update’ packet
Updates contain route prefix and metric information. They are triggered when a new route is added, a cost change occurs or a route goes down.
They are only sent to neighbours that need them
What Algorithm does EIGRP use to calculate cost to a prefix
DUAL - 5 k value metrics
Bandwidth, delay, reliability
What is the path with the lowest cost called?
The feasible distance (FD)
The router with the lowest FD is the successor router.
How does EIGRP ensure fast convergence when a router goes offline?
EIGRP elects a feasible successor and install this route in its routing table as a backup to the successor router.
What does it mean when an EIGRP route is active?
The DUAL algorithm is actively computing a cost to the prefix
What kinds of packets are sent when a route is active or in flux
Queries and replys
What value does EIGRP set the FD of a route stuck in active
Infinity - a route of infinity will allow any new advertised distance to be installed as a successor.
What does it mean when a EIGRP route is passive
The DUAL algorithm has arrived on a successor route to the prefix
What is the default or “active” timer for an EiGRP query packet
3 minutes
What happens when a route becomes stuck-in-active?
The router resets its adjacency with the neighbour router being queried
What happens when EIGRP has 2 equal cost routes to a prefix?
EIGRP will use ECMP (equal cost multi pathing) and install both routes in the routing table
What is the default number of successor routes EIGRP will install in its routing table?
4
This can be changed between 1-32
How can you prevent EIGRP from using ECMP routes
By manipulating k values to modify cost (bandwidth/delay)
What is CISCO express forwarding?
CEF is the default switching method used by routers to forward packets.
It is dependant on the FIB and Adjacency table
What data does the forward information base hold?
The FIB contains the prefix of a route, the out going interface and next hop IP address.
What does the adjacency table hold?
The adjacency table holds the protocol information (IP, IPv6), outgoing interface and precomputed layer 2 header.
What is process switching?
Process switching involves referencing the routing table for each switched packet.
CPU intense!
How do you enable unequal cost multi path in EIGRP
Using the variance metric multiplier
“Variance” command
