EIGRP = Enhanced Interior Gateway Routing Protocol
It is a Cisco proprietary, Advanced Distance Vector metric. Some folks may refer to it as a hybrid routing protocol, but it is truly not. EIGRP uses Hello packets, much like a link state protocol
Advertised distance - EIGRP metric for blank to reach network
Feasible distance - the metric to reach neighbor + the advertised distance
Features of EIGRP
Rapid convergence using Diffuse Update Algorithm (DUAL) guarantees loop free paths and backup paths. If the primary route in the table fails, the best backup route is added to the table immediately. If no route exists, EIGRP queries the neighbors.
Reduced bandwidth by not sending the entire database and instead using:
Partial updates: only include route changes, incremental updates and not the whole table
Bounded updates: only send updates to routers affected
Multiple Network Layer Support can do Appletalk, IP, IPv6, Novell (IPX)
Less Overhead by using multicast and unicast, not broadcast. The ip address 224.0.0.10 is listed in my notes
Classless Routing
The mask is advertised for each network as this provides smaller subnets and efficient use of IP addresses. The protocol can also support discontiguous subnets and VLSM (variable length subnet masks)
Load Balance
The protocol allows load balancing on equal (by default) and unequal cost paths. Caveat, for unequal cost paths, variance must be specified.
EIGRP does equal metric load balancing by default up to four equal metric routes. This means the variance value is 1 (default). The routing table can have 16 entries for the same destination.
Configuring EIGRP
usage: conf t
router eigrp 100 (automonous system 100, 1 to 65535 possible)
network 10.0.0.0
network 192.168.10.0 0.0.0.15 (the wildcard mask can advertise subnets now)
no auto-summary (what does this do?)
variance 2
Verifiy EIGRP
show ip route eigrp
show ip protocols
show ip eigrp interfaces
show ip eigrp int fa 0/0
show ip eigrp int 100
show ip eigrp topology
show ip eigrp topology all-links
show ip eigrp traffic (this command lists number of packets sent/ received; HELLO, updates, queries, replies, ack etc)
More about the Variance Command
This command allows unequal metric load balancing, metrics being
* bandwidth
* delay
* reliability - the most reliable based on keepalives
* load
* K value - calculation method and AS number must match
Troubleshoot EIGRP
show ip eigrp neighbors
show ip int brief (shows which interfaces are active)
show ip int fa 0/0 (see ip subnets)
show ip protocols (see routing for networks)
show ip eigrp int (check for the process id and the same K method)
debug eigrp packets
show ip route (displays all the routes and eigrp is labeled)
show ip eigrp topology (shows the router id with the highest IP address which should be the loopback 0)
Showing posts with label Routing Protocol. Show all posts
Showing posts with label Routing Protocol. Show all posts
Friday, March 16, 2012
Monday, March 12, 2012
ICND 2 Flashcard: Routing OSPF
This material on link-state routing protocols is supposed to be ICND2 but I'm just gonna say that you should still study this for ICND1 because I said so, and wish I did. Hello!
OSPF Configuration Commands
usage: conf t
router ospf 100 (numbers 1 to 65535 valid)
log-adjacency-changes
network ipaddressofnetwork wildcardmask area number
network 10.1.1.0 0.0.0.255 area 0
router-id
Create a router's interface loopback 0 address first
Turn on OSPF
If the IP address ever changes, use the command, clear ip ospf proces
1) This part can be configured here, else
2) Choose the highest of loopback interfaces, else
3) Choose the highest of active interfaces
Verification of OSPF working
show ip route (shows all the routes the router knows and how they are learned, O = OSPF)
show ip protocols
show ip ospf (displays general information)
show ip ospf interface (area id, adjacency info)
show ip ospf neighbor ipaddress mask
The command, show ip route, is very useful because it also shows the interface of the learned routes. I had a scenario to set up two encrypted tunnels for redundancy. I did a show ip route from router2 and I noticed that all the networks I was looking and learned from OSPF were listed; I was quite perplexed that the routes were not learned from the secondary tunnel associated with router2. Everyone thought I was quite the wizard to get all the systems green again, high fives all around, and no one really cared to listen what I was still concerned about.
Eventually I figured out that the routes were obviously learned by OSPF through the interface to router1 whose tunnel is indeed up, which verifies OSPF learned routes to distant networks works but my intended secondary tunnel was not up. I did some digging and discovered I was missing the tunnel's source ip address in the interface tunnel configuration, what a silly rookie typo. But that's proof that OSPF was working so well I had fooled everyone (but not myself).
Logically, a hub and spoke topology or partial mesh? You be the judge.
Authentication of OSPF
service password-encryption (otherwise the key will be in plaintext)
ip ospf authentication-key plainpas
ip ospf authentication OR
area 0 authentication (you can choose md5)
Troubleshooting OSPF
Consider possible errors in neighbor adjacency's, routing table, and authentication.
The authentication methods are 0 = null, 1 = simple pssword, 2 = md5
OSPF means Open Standard Shortest Path First
- It is Classless IGP within a larger AS operating as a single OSPF network on Cisco
- A Link State protocol propagates the LSA's and not routing table updates
These are flood to all OSPF interfaces in the area
- the description of the interface
- advertises immediately state changes
- periodic update of entire database in 30 minutes
- forms a link state database
- calculates the shortest path using a SPF algorithm
- all routers in the area will have the same topological database; knowledge of distant routers
HELLO Protocol
- OSPF sends hello packets on an interface and confirms to OSPF routers the presence of another OSPF on the link, with each other
- bidirectional response
- adjacency is formed when two routers agree on area-id, hello/dead interval, authentication, stub, area flags
To reduce traffic there is one router chosen as the DR (designated router), a BDR (backup designated router) and the rest are DROTHERS. The multicast ip address is used 224.0.0.5 and the router id used is the loopback interface.
COST
To calculate the cost of the link, use the reference bandwidth/ interface bandwidth in bits per second. For link speed greater than 100 Mbps use the ospf auto-cost reference-bandwidth.
http://ccie11440.blogspot.com/2007/11/why-are-some-ospf-routes-in-database.html
OSPF Configuration Commands
usage: conf t
router ospf 100 (numbers 1 to 65535 valid)
log-adjacency-changes
network ipaddressofnetwork wildcardmask area number
network 10.1.1.0 0.0.0.255 area 0
router-id
Create a router's interface loopback 0 address first
Turn on OSPF
If the IP address ever changes, use the command, clear ip ospf proces
1) This part can be configured here, else
2) Choose the highest of loopback interfaces, else
3) Choose the highest of active interfaces
Verification of OSPF working
show ip route (shows all the routes the router knows and how they are learned, O = OSPF)
show ip protocols
show ip ospf (displays general information)
show ip ospf interface (area id, adjacency info)
show ip ospf neighbor ipaddress mask
The command, show ip route, is very useful because it also shows the interface of the learned routes. I had a scenario to set up two encrypted tunnels for redundancy. I did a show ip route from router2 and I noticed that all the networks I was looking and learned from OSPF were listed; I was quite perplexed that the routes were not learned from the secondary tunnel associated with router2. Everyone thought I was quite the wizard to get all the systems green again, high fives all around, and no one really cared to listen what I was still concerned about.
Eventually I figured out that the routes were obviously learned by OSPF through the interface to router1 whose tunnel is indeed up, which verifies OSPF learned routes to distant networks works but my intended secondary tunnel was not up. I did some digging and discovered I was missing the tunnel's source ip address in the interface tunnel configuration, what a silly rookie typo. But that's proof that OSPF was working so well I had fooled everyone (but not myself).
Logically, a hub and spoke topology or partial mesh? You be the judge.
Authentication of OSPF
service password-encryption (otherwise the key will be in plaintext)
ip ospf authentication-key plainpas
ip ospf authentication OR
area 0 authentication (you can choose md5)
Troubleshooting OSPF
Consider possible errors in neighbor adjacency's, routing table, and authentication.
The authentication methods are 0 = null, 1 = simple pssword, 2 = md5
OSPF means Open Standard Shortest Path First
- It is Classless IGP within a larger AS operating as a single OSPF network on Cisco
- A Link State protocol propagates the LSA's and not routing table updates
These are flood to all OSPF interfaces in the area
- the description of the interface
- advertises immediately state changes
- periodic update of entire database in 30 minutes
- forms a link state database
- calculates the shortest path using a SPF algorithm
- all routers in the area will have the same topological database; knowledge of distant routers
HELLO Protocol
- OSPF sends hello packets on an interface and confirms to OSPF routers the presence of another OSPF on the link, with each other
- bidirectional response
- adjacency is formed when two routers agree on area-id, hello/dead interval, authentication, stub, area flags
To reduce traffic there is one router chosen as the DR (designated router), a BDR (backup designated router) and the rest are DROTHERS. The multicast ip address is used 224.0.0.5 and the router id used is the loopback interface.
COST
To calculate the cost of the link, use the reference bandwidth/ interface bandwidth in bits per second. For link speed greater than 100 Mbps use the ospf auto-cost reference-bandwidth.
http://ccie11440.blogspot.com/2007/11/why-are-some-ospf-routes-in-database.html
Wednesday, February 8, 2012
Cisco ICND1 Flashcard: Router RIP and IGRP
ICND1 Topic: RIP
ICND2 Topics: RIPv2 VLSM, single area OSPF, EIGRP
Routing is taking a packet from one device and sending it over the network to another device on a different network. Routing requires routers. Routers learn about remote networks from neighbor routers (dynamic) or programmed static routes by the administrator. All Cisco routers are classful routers, that means expecting a default subnet mask on each interface on the router, otherwise the packet will be dropped. For default routing, the command "ip classless" must be used.
Two types of interior routing protocols
Static, Default and Dynamic Routes
IP Routing requirements
On directly connected networks, hosts and routers find the destination MAC address for the destination IP addresses using ARP.
Strategies to prevent routing loops:
Split Horizon Rule: the router will not advertise a route back through the same interface from which the route was learned
Route Poisoning: to poison a route, set the metric to infinite; for RIP that number would be 16 for the maximum number of hops. When used with Split Horizon, this strategy is called Split-Horizon with Poison Reverse.
Holddown: holddown timer is used in route convergence, by preventing route from reinstating the route until all routers have enough time to "age out" the route from the tables. Prevents routes from advertising bad or expired routing information.
a) hop count based
b) link state
c) cost based
d) distance-vector
e) advanced distance-vector (hybrid)
f) bndwidth based
answer 1. b,d,e
Name two IGP (interior gateway protocol) Distance Vector protocols: RIP, IGRP (Cisco proprietary)
conf t usage:
router rip
network 192.5.5.0
network 10.0.0.0 0.255.255.255
A handy command to create an interface to learn routes but not advertise
In router config mode usage: passive-interface interface#
IGRP - Cisco Proprietary
Interior Gateway Routing Protocol. All routers within the same autonomous system should use the same AS number, and all routers should be Cisco if IGRP is used. IGRP was created to overcome the problems with RIP such as 15 hop count limit. The maximum hop count for IGRP is 255 though 100 is the default. The IGRP metric (value to calculate best route) based on bandwidth and delay of the line called a composite metric; others factors optional but not required are reliability, load, maximum transmission unit (MTU). Sends a periodic update every 90s
usage: conf t
router igrp 10
network 172.16.0.0
IGRP can load balance up to six unequal links to a remote network (RIP networks must have the same hop count to load balance).
Summary
How does RIP work in the internetwork?
RIP uses hop counts to determine the best route to a network, with an upper hop count limit of 15
Know the RIP commands
router rip
show ip route
show ip route rip
Administrative distance
Rates the trustworthiness of routing information received on a router from a neighbor; an integer between 0 to 255, where 0 is the most trusted and 255 means no traffic will pass through this route.
Default Administrative Distances
Route Source, Default Distance
Connected interface = 0
Static route = 1
EIGRP = 90
IGRP = 100
OSPF = 110
RIP = 120
External EIGRP = 170
Unknown = 255 not routable
What is AS, autonomous system
An AS is a group of routers that share the same routing information.
Know the difference between RIP and IGRP
Describe the metrics used. RIP only uses hop count.
Others are hop count, bandwidth, delay.
Three truths, from a quiz:
Routers evaluate the available paths to a destination
The routing process uses metrics and administrative distances when evaluating network paths
Dynamic routing occurs when information is learned using routing information that is obtained from routing protocols.
Note: the routing table is only displaying the information to the user
Routing table provides an ordered list of known network addresses.
Routing tables contain metrics that are used to determine the desirability of the route
Routing table associations tell a router that a particular destination is either directly connected to the router (C) or that it can reached via another router (the next-hop router or exit interface) on the way to the final destination
Link State Routing Protocols
Link state routing protocol respond quickly to network changes
Link state routing protocols send peridoic updates (link state refreshes) at long time intervals, about once every 30 minutes!!
In link state routing protocols, every router tries to build its own internap map of the network topology
ICND2 Topics: RIPv2 VLSM, single area OSPF, EIGRP
Routing is taking a packet from one device and sending it over the network to another device on a different network. Routing requires routers. Routers learn about remote networks from neighbor routers (dynamic) or programmed static routes by the administrator. All Cisco routers are classful routers, that means expecting a default subnet mask on each interface on the router, otherwise the packet will be dropped. For default routing, the command "ip classless" must be used.
Two types of interior routing protocols
Static, Default and Dynamic Routes
IP Routing requirements
- destination address and a source address
- routing table for destination
- neighbor
On directly connected networks, hosts and routers find the destination MAC address for the destination IP addresses using ARP.
Strategies to prevent routing loops:
Split Horizon Rule: the router will not advertise a route back through the same interface from which the route was learned
Route Poisoning: to poison a route, set the metric to infinite; for RIP that number would be 16 for the maximum number of hops. When used with Split Horizon, this strategy is called Split-Horizon with Poison Reverse.
Holddown: holddown timer is used in route convergence, by preventing route from reinstating the route until all routers have enough time to "age out" the route from the tables. Prevents routes from advertising bad or expired routing information.
Routing Protocols QUIZ
Most common metrics used by routing protocols to determine a network path
hop count
bandwidth - data capacity. Say 10 Mbps is better than 64 kbps leased line
delay
load
reliability - bit error rate of each network link
cost - configuraable, by default based on bandwidth
not packet length, distance.
1. What are three types of routing protocols?Most common metrics used by routing protocols to determine a network path
hop count
bandwidth - data capacity. Say 10 Mbps is better than 64 kbps leased line
delay
load
reliability - bit error rate of each network link
cost - configuraable, by default based on bandwidth
not packet length, distance.
a) hop count based
b) link state
c) cost based
d) distance-vector
e) advanced distance-vector (hybrid)
f) bndwidth based
answer 1. b,d,e
Name two IGP (interior gateway protocol) Distance Vector protocols: RIP, IGRP (Cisco proprietary)
- uses hop count as a metric
- sends entire routing table to neighbor, called routing by rumour and periodic updates
- lower CPU overhead than link-state protocols
- uses split horizon, route poisoning, and holddown to protect from routing loops
RIP - Routing Information Protocol
Configure RIP to run on the router:conf t usage:
router rip
network 192.5.5.0
network 10.0.0.0 0.255.255.255
- RIP v1 and RIP v2
- RIP Classful
- RIP v2 supports VLSM (variable length subnet mask), route authentication
- distance vector protocol
- can load balance up to 6 equal cost paths
- uses hop count as the metric. The maximum hop count is 15, therefore 16 is infinite and unreachable
- sends periodic update every 30 seconds
- RIP timers include: update, invalid, holddown, flush (and garbage collection).
A handy command to create an interface to learn routes but not advertise
In router config mode usage: passive-interface interface#
IGRP - Cisco Proprietary
Interior Gateway Routing Protocol. All routers within the same autonomous system should use the same AS number, and all routers should be Cisco if IGRP is used. IGRP was created to overcome the problems with RIP such as 15 hop count limit. The maximum hop count for IGRP is 255 though 100 is the default. The IGRP metric (value to calculate best route) based on bandwidth and delay of the line called a composite metric; others factors optional but not required are reliability, load, maximum transmission unit (MTU). Sends a periodic update every 90s
usage: conf t
router igrp 10
network 172.16.0.0
IGRP can load balance up to six unequal links to a remote network (RIP networks must have the same hop count to load balance).
Summary
How does RIP work in the internetwork?
RIP uses hop counts to determine the best route to a network, with an upper hop count limit of 15
Know the RIP commands
router rip
show ip route
show ip route rip
Administrative distance
Rates the trustworthiness of routing information received on a router from a neighbor; an integer between 0 to 255, where 0 is the most trusted and 255 means no traffic will pass through this route.
Default Administrative Distances
Route Source, Default Distance
Connected interface = 0
Static route = 1
EIGRP = 90
IGRP = 100
OSPF = 110
RIP = 120
External EIGRP = 170
Unknown = 255 not routable
What is AS, autonomous system
An AS is a group of routers that share the same routing information.
Know the difference between RIP and IGRP
Describe the metrics used. RIP only uses hop count.
Others are hop count, bandwidth, delay.
Three truths, from a quiz:
Routers evaluate the available paths to a destination
The routing process uses metrics and administrative distances when evaluating network paths
Dynamic routing occurs when information is learned using routing information that is obtained from routing protocols.
Note: the routing table is only displaying the information to the user
Routing table provides an ordered list of known network addresses.
Routing tables contain metrics that are used to determine the desirability of the route
Routing table associations tell a router that a particular destination is either directly connected to the router (C) or that it can reached via another router (the next-hop router or exit interface) on the way to the final destination
Link State Routing Protocols
Link state routing protocol respond quickly to network changes
Link state routing protocols send peridoic updates (link state refreshes) at long time intervals, about once every 30 minutes!!
In link state routing protocols, every router tries to build its own internap map of the network topology
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