The configuration of IP service category
Configurating performance parameters
The check and maintenance of the IP network
This chapter introduces the configuration of IP optional service. If you want to know the detailed method of using the IP service command mentioned in this chapter, please refer to “IP service command” section.
You can configure the below-listed optional IP service:
Configurating performance parameters
The check and maintenance of the IP network
These operations are not necessary, yet carried out according to the requirement of network.
IP
provides a series of services to control and manage IP connection. Most of these
services are provided by ICMP. ICMP packets are normally sent to the host
computer or other routers when the router or the accessing server find IP head
of packet errors. ICMP is mainly defined by RFC 792.
If you
want to manage the different aspects of IP connection, you should execute the
following related operations:
Sending ICMP unreachable packet
Sending ICMP redirected packet
Sending ICMP mask reply packet
Setting the maximum transmission unit (MTU) of IP
Allow route cache of IP on the same interface
Sending ICMP
unreachable packet
If the system receives a packet , but find it impossible to deliver it to the destination, for example, there is no corresponding route, it will send a ICMP unreachable packet to the source host computer. This function of the system is turned on by default.
If this function is turned off, the user can turn it on with the following command under interface configuring model.
command |
Purpose
|
ip
unreachables |
The
function of sending ICMP unreachable packet. |
Sending ICMP redirected packet
Sometimes,
the host computer did not select the best router, so the router that receives
the packet detect that, according to the route list, it should re-send the
packet from the interface that receives it, and then forward it to the other
router on the same
network . Under this situation, the router will inform the source host computer
to directly send the packet of the destination address to the other router,
without passing the host computer. Redirect packet requires the source host
computer to change from the original route to the more direct route suggested by
the packet. Many operating systems of the host computer will add a host computer
router in the list of routes. But, the router would rather trust the information
from the router protocol, so it will not add a host computer router according to
this information.
This function is turned on by default. But if hot backup router protocol on this interface is configured on this interface, then this function will be automatically turned off. If the configuration of hot backup router protocol is cancelled, this function will not be automatically turned on.
If this function is turned off, the user can turn the function of sending ICMP redirect packet on with the following command under interface configuration model:
command |
Purpose
|
ip
redirects |
Allow
to send ICMP redirected packet. |
Sending
ICMP mask reply packet
Sometimes
the host computer should know the network mask, for the sake of this
information, the host computer can send ICMP mask request packet. If the router
can confirm the mask of this host computer, it will reply ICMP mask reply
packet. The router will send ICMP mask reply packet under default status.
If ICMP mask request packet is demanded to be sent, the user could use the following command under interface configuration model.
command |
Purpose
|
ip
mask-reply |
Sending
ICMP mask reply packet. |
The
system support IP path MTU detection mechanism defined by RFC 1191. IP path MTU
detection enables the host computer to dynamically detect and adapt Maximum
transmit unit (MTU) length from different paths. Sometimes, the router finds the
length of received IP packet is larger than the MTU configuration set on the
packet forwarding interface, and requires to fragment the IP packet, but this IP
packet’s “unfragment” position is setting,
the packet can not be fragmented, so the packet can only be discarded. Here, the
router will send ICMP packet to inform the host computer why the forwarding
failed, and forward MTU on the interface. The host computer will reduce
the length of packet to this target address, in order to meet
the minimum MTU of this path.
If one link in the path is disconnected, other path will be employed for transmitting the packet. the minimum MTU of it may be different from the original path. Here, the router will inform the source host computer the MTU of new path. If possible, the user should adopt the minimum MTU in the path to encapsulate IP packet to the greatest extent. Hence, it can avoid fragment, and can send minimum amount of packet, consequently enhance the efficiency of communication.
Corresponding host computer should first support IP path MTU detection, then, it can adjust the length of IP packet to be delivered according to the information from the router, in order to avoid fragment in the process of forwarding.
Setting
the maximum transmission unit (MTU) of IP
Every interface has one default IP Maximum transmission unit, which is the maximum IP packet length permitted to send. If the IP packet length exceeds this value, the router will fragment the packet
The
change of the MTU value of the interface will affect the IP MTU value of
the interface. If IP MTU equals the MTU, change MTU, and IP MTU will
automatically adjust to the new MTU value. But, change IP MTU will not affect
MTU. IP MTU cannot be bigger than
the MTU set on the current interface. All devices on the same physical medium
should have same protocol MTU to enable normal communication.
command |
Purpose
|
ip
mtu bytes |
Setting
IP MTU of the interface |
The
router checks every packet’s IP header option, it supports IP header options
defined by RFC 791: strict source routing,loose
source routing, record routing and time stamp. If option errors are detected, it
will send ICMP parameter issue packet to the host computer and discard the
packet. If errors are found in the source routing process, the router will send
ICMP unreachable (source route failure) packet to the host computer.
IP
allows host computer to designate the router of IP network where packets
passess. , this is called the
source router, it can be specified in the source route option of IP header
options. The router should forward the IP packet according to this option, or
discard these packets for the sake of safety, and send ICMP unreachable (source
router failure) packet to the source host computer. Router
default supports source router. .
If the function of IP source router is turned off, the user can use the following command to allow IP source router under global configuration model:
command |
Purpose
|
ip
source-route |
Allow
IP source router. |
The route cache of IP uses route cache to forward IP packets. When forwarding the first packet towards certain destination address, the system looks up in the route table and, and forward packets according to the router. Then, this router will be saved in the route cache, all the packets to this host computer, then, will be forwarded directly according to the route in the cache rather than looking it up in the route table. The system does not form route cache according to ICMP packets and broadcasting packets, because theses packets are not sent continually. If the cache is not used, it will be deleted quickly due to its overtime.
The
route cache may not be suitable for the retransmission from high speed medium to
low speed link (64K or less), because it will speed up retransmission
speed and the packets will be more quickly stocked on the low speed interface,
more packets will be discarded. Under this situation, the user should prohibit
IP route cache on the low speed interface. The system will execute load sharing
according to source address/destination address. If many network routes exist,
route cache guarantees the packets from the same source address/destination
address to use the same route, but forwarded packets from different source
address/destination address may be sent from multiple routes, thus, the balance
load sharing is achieved. i
In order to allow or prohibit route cache , the user can use the following command under interface configuration model.
command |
Purpose
|
ip
route-cache |
Allow
route cache (to forward IP packet is transmitted by using router cache ). |
no
ip route-cache |
Prohibit
route cache; the system will execute load sharing on every packet. |
Allow
route cache of IP on the same interface
The
user can allow IP route cache on the same interface, which is, the recipient
interface is identical to the sending interface. Normally, it
is not recommended to invoke this
function, because it conflicts with the function of redirecting of the router.
If the user has a not fully connected network, such as FR, this function can be
invoked on the FR interface. For example, router A,B,C jointly forms an FR
network, but physical links only exist between A-B and B-C, the communication
between A and C should be transferred through B: A-B-C, B receives A’s packet
from one DLCI of the interface, and then sends the packet to C through another
DLCI from the same interface.
In order to allow route cache of IP on the same interface, the user can use the following command under interface configuration model:
command |
Purpose
|
ip
route-cache same-interface |
Allow
route cache of IP packets when the sending interface is identical to the
recipient interface. |
Configurating
performance parameters
When configurating IP performance, the user should execute the following operations.
Setting TCP connection latency time
Setting TCP
connection latency time
When
the router is making TCP connection, if no links have been set up after the TCP
connection latency time is over, the router will consider the connection as a
failure, and feedback the result to the upper-level application. The user may
set the TCP connection latency time, the default value of the system is 75
seconds. This configuration has nothing to do with the TCP connection
transferred from the router, it just relates to the TCP connection set up by the
router.
The
following commands are used for setting TCP connnection latency time under
global configuration model:
command |
Purpose
|
ip
tcp synwait-time
seconds |
Set
the TCP connection latency time. |
The default TCP window size is 2000 bytes. If the user want to change the default window size, he/she can use the following command under global configuration model:
command |
Purpose
|
ip
tcp
window-size bytes |
Setting
TCP window size. |
The
user can configure IP network on X.25, FR and PPP networks. If he/she wants to
configure IP on these WANs, such as configure address mapping, etc. he/she can
refer to related documents.
The check and maintenance of the IP network
To check and maintain the network, the user should execute the following operations:
Clearing the cache, list and database
Showing the system and network statistics
Clearing the
cache, list and database
The
user can clear all contents of certain cache, list or database. If the user
thinks the statistics of certain cache, list or database is incorrect, it should
be deleted.
The
following command is used to clear incorrect items:
command |
Purposes
|
clear
tcp statistics |
Clearing
TCP statistics. |
If the
certain TCP connection needs to be closed off, the following command can
be used:
command |
Purpose |
clear
tcp {local
host-name port remote host-name port | tcb
address} |
Clearing
certain TCP connection. (TCB is TCP control block) |
Showing
the system and network statistics
The
system can show contents of cache, list and database. This information can help
to analyze condition of system resource utilization
and to solve network problems.
The
user can use the following command under managing status. Specific
method of using these commands can
be referred to Chapter of “IP service command”
命令Command |
Objective |
show
ip access-lists
name |
Showing
the content of certain or all access list. |
show
ip cache [prefix mask] [type number] |
Showing
the route cache used for quick change of IP packets. |
show
ip sockets |
Showing
all socket information of the router. |
show
ip traffic |
Showing
the statistics of IP Protocol. |
show
tcp |
Showing
all information of TCP connection situation |
show
tcp brief |
Showing
brief information of TCP connection situation |
show
tcp statistics |
Showing
TCP statistics. |
show
tcp tcb |
Showing
information of certain TCP connection situation |
When
the network encounters problems, the user can use command “debug”, to
request the system to show the debug information.
The
user can use the following command under management status. The speicif method
of using these commands can be referred to the chapter of “IP Service
Commands”.
Command |
Purpose |
debug
arp |
Showing
the interactive information of Address resolution protocol (ARP) |
debug
ip icmp |
Showing
the interactive information of internet control packets protocol (ICMP) |
debug
ip raw |
Showing
the received and sent internet protocol (IP) packets. |
debug
ip packet |
Showing
the interactive information of internet protocol (IP) |
debug
ip tcp |
Showing
the interactive information of Transmission Control Protocol (TCP). |
debug
ip udp |
Showing
the interactive information of User data package protocol (UDP). |