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1. When to use multiple routing protocols?
When two different routing protocols want to exchange routing information, multiple routing protocols are used. Of course, routing redistribution can also exchange routing information. There is no need to use multiple routing protocols in the following situations:
upgrading from the old version of the Interior Gateway Protocol (Interior Gateway Protocol, IGP) to the new version of IGP.
You want to use another routing protocol but you must keep the original protocol.
You want to terminate the internal routing to avoid interference from other routers that do not have strict filtering and supervision functions.
You are in an environment composed of routers from multiple manufacturers.
1. When to use multiple routing protocols?
When two different routing protocols want to exchange routing information, multiple routing protocols are used. Of course, routing redistribution can also exchange routing information. There is no need to use multiple routing protocols in the following situations:
upgrading from the old version of the Interior Gateway Protocol (Interior Gateway Protocol, IGP) to the new version of IGP.
You want to use another routing protocol but you must keep the original protocol.
You want to terminate the internal routing to avoid interference from other routers that do not have strict filtering and supervision functions.
You are in an environment composed of routers from multiple manufacturers.
3. What is a link state routing protocol? A
link state routing protocol is more suitable for large networks, but due to its complexity, routers require more CPU resources. It can find broken links or newly connected routers in a shorter time, making the convergence time of the protocol shorter than that of the distance vector routing protocol.
Generally, if it does not receive a HELLO message from a neighboring station within 10 seconds, it considers that the neighboring station is unreachable. A link state router sends update messages to its neighbors to notify all links it knows about.
It determines that the metric value of the optimal path is a numerical cost, and the value of this cost is generally determined by the bandwidth of the link. The link with the smallest cost is considered optimal. In the shortest path first algorithm, the value of the maximum possible cost can be almost unlimited.
If there is no change in the network, the router only needs to periodically refresh the routing table that has not been updated (the period can be from 30 minutes to 2 hours).
There are several link state routing protocols: IP OSPF, IPX NLSP and IS-IS.
Can a router use both the distance vector routing protocol and the link state routing protocol?
Yes. Each interface can be configured to use a different routing protocol; but they must be able to exchange routing information by redistributing routes.
4. What is an access table? An
access table is a series of rules added by the administrator to control the input and output of data packets in the router. It is not generated by the router itself.
The access table can allow or prohibit data packets from entering or outputting to the destination.
The entry of the access table is executed in sequence, that is, when the data packet arrives, it is first to see whether it is constrained by the first entry, if not, then the sequence is executed downward; if it matches the first entry, no matter Whether it is allowed or forbidden, there is no need to perform the check of the following entries.
There can only be one access table for each protocol of each interface.
5. What types of access tables are supported?
An access table can be determined by its number. The specific protocol and its corresponding access table number are as follows:
IP standard access table number: 1～99
IP extended access table number: 100～199
IP X standard access table number: 800～899
IP X extended access table number: 1000～1099
AppleTa lk access table number: 600 ~ 699
6, how to create an IP standard access list?
create an IP standard access list can be done by the following command: access-list access list number { permit | deny} source [source-mask]
in In this command:
access list number: Determine which access list this entry belongs to. It is a number from 1 to 99.
permit | deny: Indicates whether this entry permits or blocks information traffic from a specific address.
source: Determine the source IP address.
source-mask: Determine which bits in the address are used for matching. If a bit is "1", it means that the bit in the address is ignored, if it is "0", it means that the bit in the address will be used for matching. You can use wildcards.
The following is an example of an access list in a router configuration file:
Router# show access-lists
Standard IP access list 1
deny 204.59.144.0, wildcard bits 0.0.0.255
ermit any
7. When to use route redistribution?
Route redistribution is usually configured on routers that are responsible for learning routes from one autonomous system and then broadcasting to another autonomous system. If you are using IGRP or EIGRP, route redistribution is usually performed automatically.
8. What is administrative distance?
Administrative distance refers to the routing credibility of a routing protocol. Each routing protocol assigns a trust level in turn from high to low reliability. This trust level is called administrative distance. For routing information from two different routing protocols to a destination, the router first decides which protocol to trust based on the administrative distance.
9. How to configure redistribution?
Before routing redistribution, you must first:
- Decide where to add new agreements.
- Determine the Autonomous System Border Router (ASBR).
- Decide which protocol is at the core and which is at the border.
- Decide the direction of route redistribution.
You can use the following command to redistribute routing updates (this example is for OSPF):
router(config-router)#redistribute protocol [process-id] [metric metric-value] [metric-type type-value] [subnets]
in this In the command:
◎protocol: Specify the source routing protocol of the router to redistribute routes.
The main values are: bgp, eqp, igrp, isis, ospf, static [ip ], connected and rip.
◎process-id: Specifies the process ID of OSPF.
◎metric: is an optional parameter used to specify the metric value of the redistributed route. The default metric value is 0.
8. What is administrative distance?
Administrative distance refers to the routing credibility of a routing protocol. Each routing protocol assigns a trust level in turn from high to low reliability. This trust level is called administrative distance. For routing information from two different routing protocols to a destination, the router first decides which protocol to trust based on the administrative distance.
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9. How to configure redistribution?
Before routing redistribution, you must first:
- Decide where to add new agreements.
- Determine the Autonomous System Border Router (ASBR).
- Decide which protocol is at the core and which is at the border.
- Decide the direction of route redistribution.
You can use the following command to redistribute routing updates (this example is for OSPF):
router(config-router)#redistribute protocol [process-id] [metric metric-value] [metric-type type-value] [subnets]
in this In the command:
◎protocol: Specify the source routing protocol of the router to redistribute routes.
The main values are: bgp, eqp, igrp, isis, ospf, static [ip ], connected and rip.
◎process-id: Specifies the process ID of OSPF.
◎metric: is an optional parameter used to specify the metric value of the redistributed route. The default metric value is 0.
