Recursive routing of Advanced Static routes by (iii)

Recursive queries for routing are not necessary for dynamic routing in terms of static routes. The purpose of using recursive routing is to bypass those frequently changing links, which can reduce the configuration effort of static routes.

First, the experimental topology

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Second, the experimental explanation

1, R1 If you want to communicate with R4, R1 must have a static route to R4, if the simple topology, a number of static routes can, if the link to the R4 there are many, or frequent changes, you need to write a large number of static routes to ensure communication. In order to reduce the workload, you can use recursion.

2, the implementation of recursive routing is the static route directly associated with the target network segment router inbound interface IP address.

3, the implementation of asymmetric routing. R1 ICMP echo packet and R4 ICMP reply package use a different path.

Third, the experimental steps

1. Configure static routes on the R1,R4.

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2, when the R1 received data to 4.4.4.0/24, query the route table, from f0/0, but only know the next hop address 20.1.1.4, at this time R1 send ARP broadcast to f0/0, query MAC address. What happens when R2 and R3 receive ARP broadcasts? By default, R2 and R3 both have proxy ARP turned on, and a arp-replay packet is sent to the ARP record that has that address in the local ARP table. But the R1 found that R1 did not record 20.1.1.4 of the MAC address in the ARP table, but is discarded, this is why? Because R1 will first determine whether the respondent's network segment can be reached (note: The PC is unconditionally received Proxy-arp reply and added to the ARP table). Another problem is that R2 and R3 have received the ARP broadcast, R1 will choose to go R2 or R3?

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3, configure the static route to 20.1.1.0/24 on the R1, configure the static route to 10.1.1.0/24 on the R4. At this point, ping 4.4.4.4, found that the ARP table entry has a 20.1.1.4 record, found to be R2 F0/0mac address. After R1 sends an ARP broadcast, both R1 and R2 send a arp-reply package, who, after that, writes the MAC address to the record table. Therefore, the address of the next hop node of the recursive table query does not affect the selection of the path, and the path selection is proxy ARP.

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4, how to implement asymmetric routing it? ARP table entry default save time is 4 hours, but after 4 hours, then resend Arp-echo packet, then go to 4.4.4.0/24 is to go R2 or R3 have randomness. At this point we may implement asymmetric routing by modifying the ARP expiration time and the proxy ARP feature of the shutdown interface.

R2 (config-if) #no IP proxy-arp

R3 (config-if) #no IP proxy-arp

5, although the proxy ARP is disabled, when the data arrives at the specified router does not go to the destination segment of the route, at this time you need to add static routes in R2 and R3. Verify the results by crawling the packages on the link.

R2 (config) #ip Route 1.1.1.0 255.255.255.0 f0/0 10.1.1.1

R3 (config) #ip Route 4.4.4.0 255.255.255.0 F0/1 20.1.1.4

R2 to R1 the link clutch result is all reply type of package, R3 to the R4 link is all request package, the successful implementation of asymmetric routing.

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Recursive routing of Advanced Static routes by (iii)