Download CCNP Routing Semester 5

CCNP Routing
Semester 5
Chapter 3
Routing Overview
Protocols and Metrics
Protocol
Metric
RIPv1
Hop count
IGRP
Bandwidth, delay, load, reliability, MTU
EIGRP
Bandwidth, delay, load, reliability, MTU
OSPF
Cost (the Cisco default states the cost of
an interface is inversely proportional to
the bandwidth of the interface. A higher
bandwidth indicates a lower cost)
IS-IS
Cost
Protocols and Codes
Code
I
D
EX
R
C
S
E
B
L ???
Protocol
IGRP
EIGRP
External EIGRP
RIP
Connected
Static
EGP
BGP
IS-IS
Protocols and Codes
L1
IS-IS Level 1
L2
IS-IS Level 2
M
Mobile
U
Per user static route
O
ODR
T
Traffic-engineered route
O
OSPF Networks from within the same
area as the router. These are networks
learned from router and network LSAs
OSPF Codes
IA ??
OSPF interarea. This is sent out by the
ABRs and is created from the summary
link (LSA type 3 and 4). These routes
will not bee seen on a router within a
totally stubby area because it will not
receive LSAs external to the area.
N1
OSPF NSSA external type 1
N2
OSPF NSSA external type 2
OSPF Codes
E1
OSPF external type 1 – generated by
ASBR and show routes that are external
to AS. Cost is summarization of external
cost plus the cost of the path to the
ASBR. Will not be seen in a stub or
totally stubby area.
E2
OSPF external type 2 – these routes do
not take into account the cost of the path
to the ASBR – consider only external
cost
Distance Vector Characteristics
• Sends entire routing table at periodic intervals out
all interfaces – will also send triggered updates to
reflect changes in network
• Involves updates sent using a broadcast address to
everyone on the link
• Uses metric based on how distant the remote
network is to the router – IGRP does not conform
• Has knowledge of the network based on
information learned from neighbors
• Includes a routing table that is database viewed
from perspective of each router
Distance Vector Characteristics
• Uses Bellman Ford algorithm for calculating best
path
• Does not consume many router resources – but is
heavy in use of network resources
• Maintains one domain in which all routes are
known
• Is not restricted by addressing scheme
• Involves slower convergence – each routing table
on every intervening router must be updated
before changes reach remote end of network
Link State Characteristics
• Sends incremental updates when a change is
detected – OSPF will send summary info every 30
minutes, regardless of incremental updates
• Typically involves updates sent to those routers
participating in the routing protocol domain, via a
multicast address
• Is capable of using a complex metric, referred to
as cost
• Has knowledge of network based on info learned
from every router in the area
Link State Characteristics
• Has topological database that is the same for every
router in the area – table unique to each router
• Uses Dijkstra algorithm
• Uses many router resources but is relatively low in
its demand for network resources
• Has hierarchical design of areas that allow for
summarization and growth
• For effective use, the addressing scheme should
reflect hierarchical design of network
• Quicker convergence because update is flooded
immediately throughout the network
Differences Between
RIPv1 and OSPF
RIPv1
• Simple protocol to design,
configure and maintain
• Does not require a
hierarchical address
• Does not pass the subnet
mask in the routing
update; can’t handle
classless routing or VLSM
OSPF
• Complex to design,
configure and maintain
• Requires hierarchical IP
addressing scheme if full
benefits are to be
harnessed
• Carries the mask in the
update; can implement
VLSM, summarization
and classless routing
Differences Between
RIPv1 and OSPF
RIPv1
• Is limited to 15 hops
• Does not acknowledge
updates; repeats them
periodically every 30 sec.
• Has a routing table that is
sent out of every interface
every 30 seconds
OSPF
• Unlimited in diameter of
network; it is suggested
area not exceed 50
networks
• Acknowledges updates
• Involves updates sent as
required (when changes
are seen) and every 30
minutes after no change
has been seen
Differences Between
RIPv1 and OSPF
RIPv1
• Can transmit info in two
messages – routing update
and triggered update
• Uses hop count as metric
OSPF
• Has protocols for
discovering neighbors and
forming adjacencies as
well as protocols for
sending updates through
the network – these
protocols alone add up to
nine message types
• Uses cost as a metric –
cost has the capacity to be
a complex calculation; not
defined in RFCs
Administrative Distance Values
Connected interface or static route that IDs
outgoing interface
Static route
EIGRP summary route
External BGP ??
EIGRP
IGRP
OSPF
RIP
External EIGRP
External BGP ??
An unknown network
0
1
5
20
90
100
110
120
170
200
255 or infinity
Static Routing Advantages
• Low processor overhead – routers don’t
spend valuable CPU cycles calculating the
best path. This requires less processing
power and less memory (and, therefore, a
less expensive router)
• No bandwidth utilization – routers don’t eat
up bandwidth updating each other about
static routes
Static Routing Advantages
• Secure operation – routers that don’t send
updates won’t inadvertently advertise
network information to an untrusted source.
Routers that don’t accept routing updates
are less vulnerable to attack
• Predictability – static routes enable an
administrator to precisely control a router’s
path selection. Dynamic routing often
yields unexpected results, even in small
networks
Static Routing Disadvantages
• High-maintenance configuration –
administrators must configure all static
routes manually. Complex networks
may require constant reconfiguration
• No adaptability – statically configured
routes can’t adapt to changes in link
status
Dynamic Routing Advantages
• High degree of adaptability – routers can
alert each other about downed links or
newly discovered paths. Routers
automatically “learn” a network’s topology
and select optimum paths
• Low maintenance configuration – after the
basic parameters for a routing protocol are
set correctly, administrative intervention is
not required
Dynamic Routing Disadvantages
• Increased processor overhead – dynamic
routing processes can require a significant
amount of CPU time and system memory
• High bandwidth utilization – routers must
use bandwidth to send and receive routing
updates, which can detrimentally affect
performance on slow WAN links
Configuring Static Routing
• Using an Exit Interface
– RTA (config)#ip route 10.6.0.0 255.255.0.0 s1
• Using a Next-Hop IP Address
– RTA (config)#ip route 10.7.0.0 255.255.0.0 10.4.0.2
Glossary
Adjacent
Neighbors
Router directly connected; must have
same mask and hello parameters; can
exchange routing information
Area
A logical set of network segments and
their attached devices, usually connected
to other areas via routers making a single
AS
Autonomous
Switching
Feature on Cisco router that provides
faster packet processing by allowing
ciscoBus to switch packets independently
without interrupting the system processor
Glossary
Berkeley
Standard
Distribution
Term used to describe any of variety of
UNIX-type OS based on UC Berkeley
BSD operating system
Cisco
Express
Forwarding
Advanced layer 3 IP switching
technology. CEF optimizes network
performance and scalability for networks
with large and dynamic traffic patterns
such as the Internet, on networks
characterized by intensive web-based
applications or interactive sessions
Glossary
Classful
Routing
Protocol
Protocol that does not carry the subnet
mask; usually distance vector; does not
allow implementation of VLSM and
summarization
Classless
Routing
Protocol
Carries subnet mask in the routing
update; allows implementation of VLSM
and summarization
Glossary
Convergence
Speed and capability of a group of
internetworking devices running a
specific routing protocol to agree on the
topology of an internetwork after a
change in that topology
Count to
Infinity
Problem that can occur in routing
algorithms that are slow to converge, in
which routers continuously increment the
hop count to particular networks.
Typically, some hop count limit is
imposed to prevent the problem
Glossary
Default
Routes
Route that should be used in the
destination network is not present in the
routing table
Diffusing
Update
Algorithm =
DUAL
Convergence algorithm used in Enhanced
IGRP that provides loop-free Operation at
every instant throughout a route
computation. This allows routers
involved in a topology change to
synchronize at the same time, while not
involving routes that are unaffected by
the change
Glossary
Dijkstra
Algorithm
Iterates on length of path to determine a
shortest path spanning tree. Used in LSA
– sometimes called shortest path first
algorithm
Distance
Vector
Protocol
Iterates on number of hops in route to
find shortest path spanning tree. Call for
each router to send entire routing table in
each update, but only to its neighbors.
Can be prone to routing loops but
computationally simpler than LSA. Uses
Bellman Ford routing algorithm
Glossary
Dynamic
Routes
Automatic rerouting of traffic based on
sensing and analyzing current actual network
conditions, not including cases of routing
decisions taken on predefined info
Exterior
Routing
Used to exchange info between AS or
organizations, used to connect to Internet;
BGP and EGP are examples
Fast
Cache in Cisco router that contains routing
Switching decisions. After routing decision for a packet
made, it can be cached in any one of a variety
of caches. Enhances forwarding of traffic
Glossary
Feasible
Describes next hop router that has path to
Successor remote network that EIGRP considers a
viable route
Flash
Update
Sent asynchronously in response to change in
network topology. If there is a change in
metric, update sent immediately without
waiting for timer to expire; aka triggered
updates
Floating
Static
Route
Manually configured; identified as route to
choose only if dynamically learned routes
fail. Requires higher admin distance than
routing protocol being used
Glossary
Flooding
Traffic-passing technique used by
switches and bridges to send out frame
through all interfaces except port on
which received
Incremental
Update
Sent only when there is a change in
topology
Interior
Routing
Protocol
Used to route information between
routers in AS
Glossary
Link-state
Broadcast packet used by link-state
Advertisement protocols that contains info about
neighbors and path costs. Used by
receiving routers to maintain routing
tables
Link-state
Algorithm
Each router broadcasts or multicasts info
regarding the cost to reach each of its
neighbors to all nodes in the network
Neighbor
In OSPF or EIGRP, two routers that have
interfaces to a common network
Glossary
Poison
Reverse
Routing updates that specifically indicate that
a network or subnet is unreachable, rather
than implying that a network is unreachable
by not including it in updates
Redistribution
Allowing routing info discovered through
one routing protocol to be distributed in the
update messages of another routing protocol.
Sometimes called route redistribution
Routed
Protocol
Protocol that can be routed – AppleTalk,
DECnet, IP, IPX
Glossary
Routing
Function
Process of finding a path to a destination host
Routing
Loop
Loop in which routing info is fed back to
originating router; often happens when
redistribution is configured; can lead to
confusion if originating router loses the route
– it may believe there is an alternate path
Routing
Protocol
Accomplishes routing through the
implementation of a specific algorithm –
IGRP, OSPR, RIP
Glossary
Silicon
Based on Silicon Switch Engine (SSE) which
Switching allows the processing of packets independent
of the Silicon Switch Processor (SSP);
provides high speed, dedicated packet
switching
Split
Horizon
Rules
Routing technique in which info about routes
is prevented from existing the router interface
through which that info was received. Useful
to prevent loops in small networks
Static
Route
Explicitly configured and entered into routing
table
Glossary
Switching Forwarding packets from an inbound
Function interface to an outbound interface
Topology
Table
Used by EIGRP and OSPF; table that records
all the routes in the network before
determining which will be entered into the
routing table
Triggered Sent asynchronously in response to change in
Update
network topology. Same as flash update