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Configure Basic Functions of the IP Protocol

In the TCP/IP protocol stack, the IP protocol is the network layer core protocol that is responsible for network interconnection. The IP protocol is a connectionless protocol. Before transmitting data, you need not set up a connection. The IP protocol tries best to deliver packets, but is does not ensure that all packets can reach the destination orderly.

Configuration Condition

None

Configure the Depth of the IP Packet Receiving Queue

The IP packets received by a device are first cached in the IP packet receiving queue of an interface. The system reads packets orderly in the queue for processing. If the cached IP packets reach the specified queue depth, the later IP packets are discarded. You can adjust the depth of the IP packet receiving queue according to burst of IP packets in the network.

Table 2-5 Configuring the Depth of the IP Packet Receiving Queue

Step

Command

Description

Enter the global configuration mode.

configure terminal

-

Configure the depth of the IP packet receiving queue to a specified value.

ip option queue-length queue-size

Mandatory.

By default, the depth of the IP packet receiving queue is 200.

Configure the depth of the IP packet receiving queue to the default value.

default ip option queue-length

Optional.

Configure the TTL of Transmitted IP Packets

The header of an IP packet contains the Time-To-Live (TTL) field, which is decreased by one once the IP packet passes a routing device. When the TTL is 0, the device discards the IP packet. By default, the TTL of IP packets transmitted by the device is 255, that is, the packet can only be transmitted for up to 255 times. If you want to limit the number of packet forwarding times, adjust the TTL value for the transmitted IP packets.

Table 2-6 Configuring the TTL of Transmitted IP packets

Step

Command

Description

Enter the global configuration mode.

configure terminal

-

Configure the TTL of transmitted IP packets to a specified value.

ip option default-ttl ttl-value

Mandatory.

By default, the TTL of transmitted IP packets is 255.

Configure the TTL of transmitted IP packets to a default value.

default ip option default-ttl

Optional.

Configure Timeout for Packet Reassembly

If an IP packet is fragmented during the transmission, after the fragments reach the destination, they need to be reassembled to form a complete IP packet. Before all fragments are received, the received fragments are cached temporarily. If reassembly times out before all fragments reach the destination, the received fragments are discarded.

Table 2-7 Configuring Timeout for Packet Reassembly

Step

Command

Description

Enter the global configuration mode.

configure terminal

-

Configuring timeout for packet reassembly to a specified value.

ip option fragment-ttl ttl-value

Mandatory.

By default, the timeout for packet reassembly is 60, and the unit is 0.5 second.

Configuring timeout for packet reassembly to the default value.

default ip option fragment-ttl

Optional.

note


  • The unit for timeout of packet reassembly is 0.5 second.

     

Enable IP Packet Receiving Verification and Check

You can enable this function to verify and check the received IP packets. If the checksum is incorrect, the packet will be discarded.

Table 2-8 Enabling IP Packet Receiving Verification and Check

Step

Command

Description

Enter the global configuration mode.

configure terminal

-

Enable IP packet receiving verification and check.

ip option recv-checksum

Mandatory.

By default, the function is enabled.

Configure the method for verifying and checking the received IP packets to the default value.

default ip option recv-checksum

Optional.

Enable IP Routing Cache

After a packet is sent from socket to the IP layer, if the destination address is the same as the previous packet and the route is valid, the packet directly use the route in the cache without the need of searching for another route.

Table 2-9 Enabling IP Routing Cache

Step

Command

Description

Enter the global configuration mode.

configure terminal

-

Enable IP routing cache.

ip upper-cache

Mandatory.

By default, the IP routing cache function is enabled.