1.1 IP Addressing Overview
1.1.1 IP
Address Classes
IP addressing uses a 32-bit address to
identify each host on a network. An example is 01010000100000001000000010000000
in binary. To make IP addresses in 32-bit form easier to read, they are written
in dotted decimal notation, each being four octets in length, for example, 10.1.1.1
for the address just mentioned.
Each IP address breaks down into two parts:
l
Net ID: The first several bits of the IP address
defining a network, also known as class bits.
l
Host ID: Identifies a host on a network.
For administration sake, IP addresses are
divided into five classes, as shown in the following figure (in which the blue
parts represent the address class).
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 quantity.
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.
|
The following IP addresses are for special
use, and they cannot be used as host IP addresses:
l
IP address with an all-zeros net ID: Identifies
a host on the local network. For example, IP address 0.0.0.16 indicates the
host with a host ID of 16 on the local network.
l
IP address with an all-zeros host ID: Identifies
a network.
l
IP address with an all-ones host ID: Identifies a
directed broadcast address. For example, a packet with the destination address of
192.168.1.255 will be broadcasted to all the hosts on the network 192.168.1.0.
1.1.3 Subnetting and Masking
Subnetting was developed to address the
risk of IP address exhaustion resulting from fast expansion of the Internet.
The idea is to break a network down into smaller networks called subnets by
using some bits of the host ID to create a subnet ID. To identify the boundary
between the host ID and the combination of net ID and subnet ID, masking is
used.
Each subnet mask comprises 32 bits related
to the corresponding bits in an IP address. 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.
Figure 1-2 shows how a
Class B network is subnetted.
Figure 1-2 Subnet a Class B network
While allowing you to create multiple
logical networks within a single Class A, B, or C network, subnetting is
transparent to the rest of the Internet. All these networks still appear as
one. As subnetting adds an additional level, subnet ID, to the two-level
hierarchy with IP addressing, IP routing now involves three steps: delivery to
the site, delivery to the subnet, and delivery to the host.
In the absence of subnetting, some special addresses
such as the addresses with the net ID of all zeros and the addresses with the
host ID of all ones, are not assignable to hosts. The same is true of subnetting.
When designing your network, you should note that subnetting is somewhat a
tradeoff between subnets and accommodated hosts. For example, a Class B network
can accommodate 65,534 (216 – 2. Of the two deducted Class B
addresses, one with an all-ones host ID is the broadcast address and the other with
an all-zeros host ID is the network address) hosts before being subnetted.
After you break it down into 512 (29) subnets by using the first 9 bits
of the host ID for the subnet, you have only 7 bits for the host ID and thus
have only 126 (27 – 2) hosts in each subnet. The maximum
number of hosts is thus 64,512 (512 × 126), 1022 less after 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
S3100 Series Ethernet Switches support
assigning IP addresses to VLAN interfaces and loopback interfaces. Besides
directly assigning an IP address to a VLAN interface, you may configure a VLAN interface
to obtain an IP address through BOOTP or DHCP as alternatives. If you change
the way an interface obtains an IP address, from manual assignment to BOOTP for
example, the IP address obtained from BOOTP will overwrite the old one manually
assigned.
This chapter only covers how to assign an IP address manually. For the
other two approaches to IP address assignment, refer to the part discussing DHCP
in this manual.
Table 1-2
Configure an IP address to an interface
|
Operation
|
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 }
|
Required
No IP address is assigned by default.
|
l
A newly specified IP address overwrites the previous
one if there is any.
l
The IP address of a VLAN interface must not be
on the same network segment as that of a loopback interface on a device.
After the above configuration, you can
execute the display command in any view to display the operating status
and configuration on the interface to verify your configuration.
Table 1-3
Display IP addressing configuration
|
Operation
|
Command
|
Remarks
|
|
Display information about a specified or
all Layer 3 interfaces
|
display ip interface [ interface-type interface-number ]
|
Available
in any view
|
|
Display brief configuration information about
a specified or all Layer 3 interfaces
|
display ip interface brief [ interface-type [ interface-number ]
]
|
1.4 IP Address Configuration Examples
I. Network requirement
Assign IP address 129.2.2.1 with mask
255.255.255.0 to VLAN interface 1 of the switch.
II. Network diagram
Figure 1-3 Network diagram for IP
address configuration
III. Configuration procedure
# Configure an IP address for VLAN interface
1.
<Switch> system-view
[Switch] interface Vlan-interface 1
[Switch-Vlan-interface1] ip address 129.2.2.1
255.255.255.0
2.1 IP Performance Overview
In some network environments, you need to
adjust the IP parameters to achieve best network performance. The IP
performance configuration supported by S3100 Series Ethernet Switches includes:
l
Configuring TCP attributes
l
Disabling ICMP to send error packets
Every switch stores a forwarding
information base (FIB). FIB is used to store the forwarding information of the switch
and guide Layer 3 packet forwarding.
You can know the forwarding information of
the switch through the FIB table. Each FIB entry includes: destination
address/mask length, next hop, current flag, timestamp, and outbound interface.
When the switch is running normally, the
contents of the FIB and the routing table are the same.
2.2 Configuring IP Performance
Table 2-1
Introduction to IP performance configuration tasks
|
Configuration task
|
Description
|
Related section
|
|
Configure TCP attributes
|
Optional
|
2.2.2
|
|
Disable ICMP to send error packets
|
Optional
|
2.2.3
|
TCP optional parameters that can be configured
include:
l
synwait timer: When sending a SYN packet, TCP
starts the synwait timer. If no response packets are received before the
synwait timer times out, the TCP connection is not successfully created.
l
finwait timer: When the TCP connection is changed
into FIN_WAIT_2 state, finwait timer will be started. If no FIN packets are
received within the timer timeout, 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, the system restarts the timer from receiving the
last non-FIN packet. The connection is broken after the timer expires.
l
Size of TCP receive/send buffer
Table 2-2
Configure TCP attributes
|
Operation
|
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 receive/send
buffer
|
tcp window window-size
|
Optional
By default, the buffer is 8 kilobytes.
|
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.
By default, S3100 Series Ethernet Switches
support sending ICMP redirect and destination unreachable packets.
Although sending ICMP error packets
facilitate control and management, it still has the following disadvantages:
l
Sending a lot of ICMP packets will increase
network traffic.
l
If receiving a lot of malicious packets that cause
it to send ICMP error packets, the device’s performance will be reduced.
l
As the ICMP redirection function increases the
routing table size of a host, the host’s performance will be reduced if
its routing table becomes very large.
l
If a host sends malicious ICMP destination
unreachable packets, end users may be affected.
You can disable the device from sending
such ICMP error packets for reducing network traffic and preventing malicious
attacks.
Table 2-3
Disable sending ICMP error packets
|
Operation
|
Command
|
Remarks
|
|
Enter system view
|
system-view
|
—
|
|
Disable sending ICMP redirects
|
undo icmp redirect send
|
Required
Enabled by default
|
|
Disable sending ICMP destination
unreachable packets
|
undo icmp unreach send
|
Required
Enabled by default
|
After the above configurations, you can
execute the display command in any view to display the running status to
verify your IP performance configuration.
Use the reset command in user view
to clear the IP, TCP, and UDP traffic statistics.
Table 2-4
Display and maintain IP performance
|
Operation
|
Command
|
Remarks
|
|
Display
TCP connection status
|
display
tcp status
|
You can execute the display command
in any view.
|
|
Display
TCP connection statistics
|
display
tcp statistics
|
|
Display
UDP traffic statistics
|
display
udp statistics
|
|
Display IP
traffic statistics
|
display
ip statistics
|
|
Display
ICMP traffic statistics
|
display
icmp statistics
|
|
Display
the current socket information of the system
|
display
ip socket [ socktype sock-type ] [ task-id socket-id ]
|
|
Display
the forwarding information base (FIB) entries
|
display
fib
|
|
Display
the FIB entries matching the destination IP address
|
display fib ip-address1 [ { mask1 | mask-length1 } [
ip-address2 { mask2 | mask-length2 } | longer ] |
longer ]
|
|
Display
the FIB entries filtering through a specific ACL
|
display fib acl number
|
|
Display the FIB entries in the buffer
which begin with, include or exclude the specified character string.
|
display fib
| { begin | include | exclude } regular-expression
|
|
Display the total number of the FIB
entries
|
display fib statistics
|
|
Clear IP traffic statistics
|
reset ip statistics
|
You can execute the reset command
in user view.
|
|
Clear TCP traffic statistics
|
reset tcp statistics
|
|
Clear UDP traffic statistics
|
reset udp statistics
|
