Reading...
Play button
Play button
Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
35 Cards in this Set
- Front
- Back
|
Static Routing
|
Admin manually adds routes into each router's routing table
|
|
|
Static routing benefits
|
- No overhead on the router CPU
- No bandwidth usage btw routers - Security (admin only lets routing to certain networks) |
|
|
Static routing disadvantages
|
- Admin must know internetworkand how each rtr is connected to config the routs
- If 1 network is added - admin must add route to all rtrs |
|
|
Command to add static route to routing table
|
ip route [destination_network] [mask] [next_hop_address or exitinterface] [administrative_distance] [permament]
|
|
|
What is "ip route" in the command to add static route to routing table?
|
The command used to create static route
|
|
|
What is the "destination_network" in command to add static route to routing table?
|
The network you are placing in the routing table
|
|
|
What is the "mask" in command to add static route to routing table?
|
The subnet mask being used on the network
|
|
|
What is the "next_hop_address" in command to add static route to routing table?
|
- The addy fo the next hop rtr that will get packet and fwd to remote network
- Is a rtr interface that is on a directly connected network - MUST be able to ping rtr inteface b/4 u add the route - If mistype or interface to that rtr is done - static rt will be in config of rtr but not in rting table. |
|
|
What is the "exit_interface" in command to add static route to routing table?
|
Used instead of next hop addy if u want - must be on pt to pt link (like WAN) - WON'T work on a LAN (like ethernet)
|
|
|
What is the "administrative_distance" in command to add static route to routing table?
|
- By default - static rts have adminstrative distance of 1
- Can change default by adidng an adminstrative weight at end of command |
|
|
What is the "permanent" in command to add static route to routing table?
|
- If interface is shut down or rtr can't communicate to next hop rtr - rt is automatically discarded from rting table
- If chose "permanent" option - it keeps entry in routing table no matter what happnes. |
|
|
What is "default routing"?
|
- Used to send packet w/ remote destination network not in routing table to next hop router.
- Can only use default rting on stub networks (only have 1 exit port out of network) |
|
|
How do you configure a "default route"?
|
-Use wildcards in the network address
|
|
|
What is a "classful router"?
|
- Rtrs that expect a default subnet mask on each interface of the router.
- When rtr gets packet for destination subnet not on rting table - drop packet by default |
|
|
What is "dynamic routing"?
|
- Protocols used to find and update routing tables on routers
|
|
|
What is "administrative distances"
|
- Used to rate trustworthiness of routing info recieve on rtr from neighbor router.
- Is integer btw 0 to 255 - 0 is most trusted - If rtr gets 2 updated listings on same remote network - 1st thing rtr checks is AD - if 1 is lower - rtr will trust that one - If have same AD - rting protocol metrics (like hop county or bandwidth) will be used to find best path. - If both had same AD and metrics - rting protocol will load balance to remote network |
|
|
What are the default admin distances for:
Connected interface Static Route EIGRP IGRP OSPF RIP External EIGRP Unknown |
0
1 89 100 119 120 170 255 |
|
|
What are the 3 classes of routing protocols?
|
Distance Vector
Link State Hybrid |
|
|
Distance Vector protocols def
|
- Finds best path to remote network by judging distance
- Route w/ least number of hops to network is best route - Vector indicates direction to remote network - RIP and IGRP are distance-vector routing protocols |
|
|
Link State Protocols
|
- rtrs each creat 3 separate tables
- 1 keeps track of directly attached neighbors - 1 determines topology of entire network - 1 is used as routing table - These routers know more about internetwork then distance-vector routers - OSPF is IP routing protocol that is completely link-state |
|
|
Hybrid Protocols
|
-Use aspects of both distance vector and like state
- EIGRP |
|
|
How do Distance-Vector Routing Protocols work?
|
- Passes complete routing tables to neighbor routers
- Neighbor routers combine recieved routing table w/ own - If network has multiple links to same remote distance - AD is checked - When rtrs start up - they only have directly connected networks in rting table - After distance-vector rting protocol is started on each protocol - rting tables are updated w/ all route info gathered from neighbor rtrs - When all rtrs are converging - no data is passed - RIP only uses hop count to determine best path - if finds more 1 link - will do round-robin load balance. |
|
|
What is pinhole congestion
|
- Sometimes in distance vector routing - have 2 links w/ equal number of hops
- 1 link has 56K connection and 1 has T1 connection - But since hopcout is only metric used w/ RIP routing they are seen as equal-cost links |
|
|
What are Routing Loops in distance-vector routing?
|
- Every router is not updated close to the same time.
- Slow convergence of distance-vector routing protocols can cause inconsistent routing tables and rting loops - If 1 router in internetwork stops working - the directly connected router is updated quick - but takes a while to get to further rtrs. - In meantime - near rtr is updating w/o the faulty network - but further networks are sending updates w/ the faulty network. |
|
|
What is "maximum hop count"?
|
- Distance vector RIP permits hop count of up to 15 - anything over is unreachable
- Keeps packets from going around routing loop forever |
|
|
What is "Split Horizon"?
|
- Another solution to routing loops
- Enforce rule that info can't be sent back in direction from which it was received. - rting protocol differentiates which interface a network route was learned on and will not advertised that route back on same interface |
|
|
What is "Route Poisoning"?
|
- If network goes down - that router starts route poisoning by entering table entry for that network of 16 (meaning unreachable)
- This way neighbor rtr is not susceptible to incorrect updates about route to down network - When neighbor rtr gets rtr poisoning update - sends update call poison reverse back to originating rtr. |
|
|
What is a "holddown"
|
- Prevents reg update msg from reinstating rt that is going up and down
- can happen on serial link that is losing connectivity and then coming back up - prevents rts from changing too rapidly by allowing time for either downed route to come back or network to stablize. 0 Also tell rtrs to restric for some time any changes that may affect recently removed routes - prevents inoperative routes from being prematurely restored to others rting tables |
|
|
What 3 instances when triggered updates will reset the holddown timer?
|
1. The holddown timer expires
2. Another update is received w/ better metric 3. A flush timer (time route would be held b4 being remove) removes route from routing table. |
|
|
RIP
|
Routing Information Protocol
- True distance-vector routing prototocl - sends complete rting table out to all active interfaces every 30 secs - Uses only hop count to determine best way to remote network - Default max hopcount is 15 - Works well in small networks - RIP v1 uses only classful routing (all dev must be on same subnet mask) - RIP v2 uses prefix routing and does send subnet mask info - ris classless routing |
|
|
3 Rip Timers
|
1. Route update timere
2. Route invalid timer 3. Route flush timer |
|
|
What is "Router Update Timers" in RIP protocol?
|
Sets interval btw periodic rting updates in which the rtr sends complete copy of its rting table out to all neighbors (typically 30 sec)
|
|
|
What is "Router Invalid Times" in RIP protocol?
|
-Determines length of time the must expire (90 s) b4 rtr determines route has become invalid
- if hasnt heard any updates about route for that period - will send out updates to all neighbors saying that route is invalid |
|
|
What is "Route Flush Timer" in RIP protocol?
|
- Sets time btw a route becomes invalid and its removal from routing table (240 s)
- B4 removed from table - notifies neighbors of the routes impending doom. - Value of route invalid time must be less then the route flush timer |
|
|
How do u configure RIP routing?
|
2521A#config t
2521A(config)#router rip 2521A(config-router)#network 172.16.0.0 |
