H3C S5500-SI Series User manual

Operation Manual – IP Address and Performance
H3C S5500-SI Series Ethernet Switches Table of Contents
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Table of Contents
Chapter 1 IP Address Configuration ...........................................................................................1-1
1.1 IP Address Overview.........................................................................................................1-1
1.1.1 IP Address Classes.................................................................................................1-1
1.2 Configuring IP Addresses..................................................................................................1-3
1.2.1 Assigning an IP Address to an Interface.................................................................1-4
1.2.2 IP Address Configuration Example.........................................................................1-4
1.3 Displaying and Maintaining IP Address Configuration....................................................... 1-6
Chapter 2 IP Performance Configuration.................................................................................... 2-1
2.1 IP Performance Overview..................................................................................................2-1
2.2 Permitting Receiving and Forwarding of Directed Broadcast Packets..............................2-1
2.2.1 Enabling Receiving of Directed Broadcasts............................................................2-1
2.2.2 Enabling Forwarding Directed Broadcasts..............................................................2-1
2.2.3 Receiving and Forwarding of Directed Broadcast Configuration Example.............2-2
2.3 Configuring TCP Attributes................................................................................................2-3
2.4 Configuring ICMP to Send Error Packets..........................................................................2-4
2.5 Displaying and Maintaining IP Performance...................................................................... 2-6

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Chapter 1 IP Address Configuration
1.1 IP Address Overview
1.1.1 IP Address Classes
Each device interface connected to the Internet must be assigned a globally unique IP
address. IP addresses are 32-bit in length, generally expressed in dotted decimal
notation. That is, an IP address can be expressed as four decimal integers separated
by dots, with each integer corresponding to one byte. 10.1.1.1 is an example.
Each IP address breaks down into two parts:
znet-id, the first several bits of the IP address defining a network, also known as
class bits.
zhost-id, identifies a host on a network.
For administration sake, IP addresses are divided into five classes. Which class an IP
address belongs to depends on the first one to four bits of the net-id, as shown in Figure
1-1.
Figure 1-1 IP address classes
Table 1-1 describes the address ranges of these five classes. Currently, the first three
classes of IP addresses are used in large quantities.

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Table 1-1 IP address classes and ranges
Class Address range Description
A 0.0.0.0 to 127.255.255.255
Address 0.0.0.0 means this host no
this network. This address is used
by a host at bootstrap when it does
not know its IP address. This
address is never a valid destination
address.
Addresses starting with 127 are
reserved for loopback test. Packets
destined to these addresses are
processed locally as input packets
rather than sent to the link.
B 128.0.0.0 to 191.255.255.255 ––
C 192.0.0.0 to 223.255.255.255 ––
D 224.0.0.0 to 239.255.255.255 Multicast address.
E 240.0.0.0 to 255.255.255.255 Reserved for future use except for
the broadcast address
255.255.255.255.
As the Internet develops rapidly, available IP addresses are being exhausted. To make
full use of available IP addresses, a network can be divided into smaller ones (known
as subnets) with subnet masks. A network can be divided into subnets by using some
bits of the host-id to create a subnet-id. The length of subnet-id is determined by subnet
mask.
A subnet mask is 32-bit in length and comprises a series of consecutive ones and a
series of consecutive zeros. In a subnet mask, the part containing consecutive ones
identifies the combination of net-id and subnet-id, whereas the part containing
consecutive zeros identifies the host-id.
A subnet is significant only within a network. From the perspective of an external
network, the network has only one net-id.Agateway performs route selection based on
subnet-id and finds the destination host only after incoming packets are received by the
network.
Figure 1-2 shows how a Class B address is subnetted.

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Figure 1-2 Subnetting a Class B address
Note that subnetting is somewhat a tradeoff between subnets and accommodated
hosts. For example, a Class B network can accommodate 65,534 hosts before being
subnetted. After you break it down into 64 subnets by using the first 6 bits of the host-id
for the subnet, you have only 10 bits for the host-id and thus have only 1,022 (210 – 2)
(excluding all-one broadcast addresses and all-zero network segment addresses)
hosts in each subnet. The maximum number of hosts is thus 64 × 1,022 = 65,408,
which is126 less than that before the network is subnetted.
Class A, B, and C networks, before being subnetted, use these default masks (also
called natural masks): 255.0.0.0, 255.255.0.0, and 255.255.255.0 respectively.
1.2 Configuring IP Addresses
An interface can obtain an IP address using the following methods:
zThrough manual IP address assignment
zThrough BOOTP
zThrough DHCP
These methods are mutually exclusive. An IP address obtained using a new method
overwrites that obtained using an old method. For example, if you manually assign an
IP address and then obtain another IP address through BOOTP, the IP address
obtained from BOOTP will overwrite the old one manually assigned. In this case, the
interface is assigned the IP address through BOOTP.
Note:
This chapter only covers how to assign an IP address manually. For how to obtain an IP
address using the other two methods, see the related sections in DHCP part of this
manual.

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1.2.1 Assigning an IP Address to an Interface
Generally, one interface is configured with one IP address. To connect multiple logical
subnets on the same physical subnet, you may assign an interface multiple IP
addresses, one primary and multiple secondary.
Follow these steps to assign an IP address to an interface:
To do… Use the command… Remarks
Enter system view system-view ––
Enter interface view interface interface-type
interface-number ––
Assign an IP address to
the interface
ip address ip-address
{ mask | mask-length }
[ sub ]
Required
No IP address is assigned
by default.
Caution:
zOne interface can be configured with only one primary IP address. The primary IP
address you assigned to the interface can overwrite the old one if there is any.
zYou cannot assign secondary IP addresses to an interface using BOOTP or DHCP.
zThe primary and secondary IP addresses you assign to the interface can be located
on the same network segment.
zWith S5500-SI series Ethernet switches, you can configure IP addresses for VLAN
interfaces and Loopback interfaces. Only 32-bit subnet masks can be configured on
Loopback interfaces.
1.2.2 IP Address Configuration Example
I. Network requirements
As shown in Figure 1-3, Vlan-interface1 (belonging to VLAN 1) on the switch is
connected to a LAN comprising two segments: 172.16.1.0/24 and 172.16.2.0/24. The
hosts in external network can communicate with the two network segments through the
switch and the hosts between the two segments can communicate with each other.

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II. Network diagram
Figure 1-3 Network diagram for IP address configuration
III. Configuration procedure
If only one IP address is configured on Vlan-interface1 of the switch, only part of the
hosts can be accessed from external network through the switch. To enable the access
to all the hosts in the network through the switch, a secondary IP address needs to be
configured for Vlan-interface1. To allow the hosts on the two segments to communicate
with each other, the switch needs to be set as the gateway on all the hosts on the two
segments.
# Assign a primary IP address and a secondary IP address to Vlan-interface1.
<Sysname> system-view
[Sysname] interface Vlan-interface 1
[Sysname-Vlan-interface1] ip address 172.16.1.1 255.255.255.0
[Sysname-Vlan-interface1] ip address 172.16.2.1 255.255.255.0 sub
# Set the gateway address to 172.16.1.1 on the PCs attached to the subnet
172.16.1.0/24, and to 172.16.2.1 on the PCs attached to the subnet 172.16.2.0/24.
# Ping a host on the subnet 172.16.1.0/24 from the switch to verify the configuration.
<Sysname> ping 172.16.1.2
PING 172.16.1.2: 56 data bytes, press CTRL_C to break
Reply from 172.16.1.2: bytes=56 Sequence=1 ttl=255 time=25 ms
Reply from 172.16.1.2: bytes=56 Sequence=2 ttl=255 time=27 ms
Reply from 172.16.1.2: bytes=56 Sequence=3 ttl=255 time=26 ms
Reply from 172.16.1.2: bytes=56 Sequence=4 ttl=255 time=26 ms
Reply from 172.16.1.2: bytes=56 Sequence=5 ttl=255 time=26 ms
--- 172.16.1.2 ping statistics ---
5 packet(s) transmitted

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5 packet(s) received
0.00% packet loss
round-trip min/avg/max = 25/26/27 ms
# Ping a host on the subnet 172.16.2.0/24 from the switch to verify the configuration.
<Sysname> ping 172.16.2.2
PING 172.16.2.2: 56 data bytes, press CTRL_C to break
Reply from 172.16.2.2: bytes=56 Sequence=1 ttl=255 time=25 ms
Reply from 172.16.2.2: bytes=56 Sequence=2 ttl=255 time=26 ms
Reply from 172.16.2.2: bytes=56 Sequence=3 ttl=255 time=26 ms
Reply from 172.16.2.2: bytes=56 Sequence=4 ttl=255 time=26 ms
Reply from 172.16.2.2: bytes=56 Sequence=5 ttl=255 time=26 ms
--- 172.16.2.2 ping statistics ---
5 packet(s) transmitted
5 packet(s) received
0.00% packet loss
round-trip min/avg/max = 25/25/26 ms
# Verify that the hosts on the subnets 172.16.1.0/24 and 172.16.2.0/24 can
communicate with each other.
1.3 Displaying and Maintaining IP Address Configuration
After the above-mentioned configuration, you can use the display command in any
view to display IP address configuration, so as to verify configuration result.
Follow these steps to display and maintain IP address configuration:
To do… Use the command…
Display information about a specified or
all L3 interfaces display ip interface [ interface-type interface-number ]
Display brief information about a
specified or all Layer 3 interfaces display ip interface brief
[ interface-type interface-number ]

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Chapter 2 IP Performance Configuration
2.1 IP Performance Overview
In some network environments, you need to adjust the IP parameters to achieve best IP
performance. IP performance configuration parameters include:
zReceiving and forwarding of directed broadcasts
zTCP timers
zSize of TCP receive/send buffer
zICMP error packets sending
2.2 Permitting Receiving and Forwarding of Directed
Broadcast Packets
Directed broadcast packets include network directed broadcast packets,
individual-subnet directed broadcast packets and all-subnet directed broadcast
packets. If a device is permitted to receive and forward directed broadcast packets,
hackers can use such packets to attack the network, which brings potential trouble to
network security. Therefore, the receiving and forwarding of directed broadcast packets
are disabled on S5500-SI series Ethernet switches by default. When necessary, you
can use the related command to permit the device to receive and forward directed
broadcast packets.
2.2.1 Enabling Receiving of Directed Broadcasts
If the device is permitted to receive directed broadcast packets, the configuration on an
interface determines whether these packets can be forwarded. Otherwise, directed
broadcast packets are discarded directly.
Follow these steps to enable the receiving of directed broadcasts:
To do… Use the command… Remarks
Enter system view system-view —
Enable the device to
receive directed
broadcasts ip forward-broadcast
Required
By default, an interface is
not allowed to receive
directed broadcasts
2.2.2 Enabling Forwarding Directed Broadcasts
Follow these steps to enable forwarding directed broadcasts:

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To do… Use the command… Remarks
Enter system view system-view —
Enter interface view interface interface-type
interface-number —
Enable forwarding
directed broadcasts
on an interface
ip forward-broadcast [acl
acl-number ]
Required
By default, directed
broadcasts forwarding is
not allowed.
Note:
zIf you have configured ACL when enabling an interface to forward directed
broadcasts, the ACL will discard the directed broadcast packets that do not meet its
rules, but forward only those in compliance with the rules.
zIf you execute the ip forward-broadcast acl command on an interface for many
times, the last executed command takes the final effect. As such, if the last
command is one without the acl acl-number, the previous ACL rules will be
cancelled.
2.2.3 Receiving and Forwarding of Directed Broadcast Configuration
Example
I. Network requirement
As shown in Figure 2-1, the PC interface and Vlan-interface3 of Switch A are in the
same network segment (1.1.1.0/24). Vlan-interface2 of Switch Aand Vlan-interface2 of
Switch B are in another network segment (2.2.2.0/24). The default gateway of the PC is
Vlan-interface3 (IP address 1.1.1.2/24) of Switch A. Configure a static route on Switch
B for the reachability between PC and Switch B.
II. Network diagram
Figure 2-1 Blocking directed broadcasts
III. Configuration procedure
zPerform the following configuration on Switch A.
# Configure Switch A to receive directed broadcast packets.

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<SwitchA> system-view
[SwitchA] ip forward-broadcast
# Configure IP addresses for Vlan-interface3 and Vlan-interface2.
[SwitchA] interface Vlan-interface 3
[SwitchA-Vlan-interface3] ip address 1.1.1.2 24
[SwitchA-Vlan-interface3] quit
[SwitchA] interface Vlan-interface 2
[SwitchA-Vlan-interface2] ip address 2.2.2.2 24
# Configure Vlan-interface2 to forward directed broadcast packets.
[SwitchA-Vlan-interface2] ip forward-broadcast
zPerform the following configuration on Switch B
# Configure Switch B to receive directed broadcast packets.
<SwitchB> system-view
[SwitchB] ip forward-broadcast
# Configure a static route from Switch B to the PC.
[SwitchB] ip route-static 1.1.1.1 24 2.2.2.2
# Configure an IP address for Vlan-interface2.
[SwitchB] interface Vlan-interface 2
[SwitchB-Vlan-interface2] ip address 2.2.2.1 24
After the above configurations, if you ping the subnet broadcast address (2.2.2.255) of
Vlan-interface 2 of Switch A on the PC, the ping packets can be received by
Vlan-interface 2 of Switch B. However, if you cancel the ip forward-broadcast
command, the ping packets can not be received by the Vlan-interface 2 of Switch B.
2.3 Configuring TCP Attributes
TCP attributes that can be configured include:
zsynwait timer: Before sending a SYN packet, TCP starts the synwait timer. If no
response packets are received before synwait timeout, TCP connection is not
successfully created.
zfinwait timer: When the TCP connection is in FIN_WAIT_2 state, finwait timer will
be started. If no FIN packets are received before the timer timeouts, the TCP
connection will be terminated. If FIN packets are received, the TCP connection
state changes to TIME_WAIT. If non-FIN packets are received, and the system
recounts the time from receiving the last non-FIN packet until the connection is
broken after the timer timeouts.
zSize of TCP receiving/sending buffer
Follow these steps to configure TCP attributes:

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To do… Use the command… Remarks
Enter system view system-view —
Configure TCP synwait
timer’s timeout value tcp timer syn-timeout
time-value
Optional
By default, the timeout
value is 75 seconds.
Configure TCP finwait
timer’s timeout value tcp timer fin-timeout
time-value
Optional
By default, the timeout
value is 675 seconds.
Configure the size of TCP
receiving/sending buffer tcp window window-size Optional
By default, the buffer is 8k
bytes.
2.4 Configuring ICMP to Send Error Packets
Sending error packets is a major function of ICMP protocol. In case of network
abnormalities, ICMP packets are usually sent by the network or transport layer
protocols to notify corresponding devices so as to facilitate control and management.
I. Advantage of sending ICMP error packets
There are three kinds of ICMP error packets: redirection packets, timeout packets and
destination unreachable packets. Their sending conditions and functions are as
follows.
1) Sending ICMP redirect packets
A host may have only one route (the default route to the default gateway) in its routing
table when starting. The default gateway will send ICMP redirect packets to the source
host and notify it to reselect a correct next hop router to send the subsequent packets,
if the following conditions are satisfied:
zThe receiving and sending interfaces are the same.
zThe selected route has not been created or modified by ICMP redirect packets.
zThe selected route is not the default route of the device.
zThere is no source route option in the packet.
ICMP redirect packets function simplifies host administration and enables a host to
gradually establish a sound routing table to find out the best route
2) Sending ICMP timeout packets
Adevice drops the data packet and sends an ICMP timeout packet to the source when
there is a timeout error after the device received an IP data packet.
The device will send an ICMP timeout packet under the following conditions:
zIf a device finds the destination of the packet is not local after receiving a data
packet whose TTL field is 1, it will send a “TTL timeout” ICMP error message.

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zWhen the device receives the first fragment IP packets whose destination address
is local, it will start the timer. If the timer timeouts before receiving all the fragments,
the device will send a “reassembly timeout” ICMP error packets.
3) Sending ICMP destination unreachable packets
Sending ICMP destination unreachable packet means when there happens a
destination timeout error after a device received an IP data packet, the device will drop
the data packet and send an ICMP error packet to the source.
The device will send an ICMP destination unreachable packet under the following
conditions:
zWhen forwarding a packet, if the device finds no corresponding forward route and
default route in the routing table, it will send a “network unreachable” ICMP error
packet.
zWhen receiving a data packet whose destination address is local, if the transfer
layer protocol is unavailable for the device, then the device sends a “protocol
unreachable” ICMP error packet.
zWhen receiving a data packet with the destination address as local and transfer
layer as UDP, if the packet’s port number does not match with the running process,
the device will send source a “port unreachable” ICMP error packet.
zWhen sending packets using “strict source routing", if the intermediate finds that
the source point to a device not directly connected to the network, it will send
source a “source routing fails” ICMP error packet.
zWhen forwarding a packet, if the MTU of the forward interface is smaller than the
packet but the packet has been set unfragmentable, the device will send source a
“fragmenting is required but unavailable” ICMP error packet.
II. Disadvantage of sending ICMP error packets
Although sending ICMP error packets facilitate control and management, it still has the
following disadvantage:
zSending a lot of ICMP packets will increase network traffic.
zIf the device receives a lot of malicious packets that sends much ICMP error
packets, it will reduce the device's performance.
zAs redirecting increases a host’s routing, it will reduce the host’s performance if
there is a great increase in the hosting.
zAs ICMP destination unreachable packets are unreachable to users' process, if
there are malicious attacks, end users may be affected.
In order to prevent such phenomena, you can disable the device from sending ICMP
error packets to reduce network traffic and avoid malicious attacks.
Follow these steps to disable sending ICMP error packets:

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To do… Use the command… Remarks
Enter system view system-view —
Disable sending ICMP
redirect packets undo ip redirects
Required
Sending a device’s ICMP
redirection packet is
enabled by default
Disable sending ICMP
timeout packets undo ip ttl-expires
Required
Sending a device’s ICMP
timeout packet is enabled
by default.
Disable sending ICMP
destination unreachable
packets undo ip unreachables
Required
Sending a device’s ICMP
destination unreachable
packet is enabled by
default
Note:
zThe device stops sending “network unreachable” and “source route unsuccessful”
ICMP error packets after sending ICMP destination unreachable packets is disabled.
But other destination unreachable packets will be sent normally.
zThe device stops sending “TTL timeout” ICMP error packets after sending ICMP
timeout packets is disabled. But “reassembly timeout” error packets will be sent
normally.
2.5 Displaying and Maintaining IP Performance
After the above-mentioned configuration, you can use the display command in any
view to display the IP performance status, so as to verify configuration result.
You can use the reset command in user view to clear the statistics about IP, TCP, and
UDP traffic.
Following these steps to display and maintain IP performance:
To do… Use the command…
Display current TCP connection state display tcp status
Display statistics of TCP connection display tcp statistics
Display statistics of UDP flows display udp statistics
Display statistics of IP packets display ip statistics
Display statistics of ICMP flows display icmp statistics

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To do… Use the command…
Display current socket information of the
system display ip socket [socktype sock-type ] [ task-id socket-id ]
Display FIB forward information display fib [ | { begin | include |
exclude } text | acl acl-number |
ip-prefix ip-prefix-name ]
Display FIB forward information
matching the specified destination IP
address
display fib ip-address1 [ { mask1 |
mask-length1 } [ ip-address2 { mask2 |
mask-length2 }| longer ] | longer ]
Display statistics about the FIB items display fib statistics
Clear statistics of IP packets reset ip statistics
Clear statistics of TCP flows reset tcp statistics
Clear statistics of UDP flows reset udp statistics