A router in this
chapter refers to a generic router or a Layer 3 switch running routing
protocols. To improve readability, this will not be described in the present
manual again.
A static route is a special route that is
manually configured by the network administrator. If a network is relatively
simple, you only need to configure static routes for the network to work
normally. The proper configuration and usage of static routes can improve a
network’s performance and ensure bandwidth for important network
applications.
The
disadvantage of static routing is that, if a fault or a topological change
occurs to the network, the route will be unreachable and the network breaks. In
this case, the network administrator has to modify the configuration manually.
A default route is a
special static route.
Generally, a router selects the default
route only when it cannot find any matching entry in the routing table. In a
routing table, the default route is in the form of the route to the network
0.0.0.0 (with the mask 0.0.0.0). You can check whether a default route has been
configured by running the display ip routing-table command.
If the destination
address of a packet fails to match any entry in the routing table, the router
selects the default route to forward the packet. If there is no default route
and the destination address of the packet is not in the routing table, the
packet will be discarded and an ICMP packet is sent to the source reporting
that the destination or the network is unreachable.
You need to be familiar with the following
contents while configuring static routes:
1)
Destination address and masks
In the ip route-static command, the
IPv4 address is in dotted decimal format and the mask can be in either dotted
decimal format or the mask length (the digits of consecutive 1s in the mask).
2)
Output interface and the next hop address
While configuring static routes, you can
specify either the output interface or next hop address. Whether you should
specify the output interface or the next hop address depends on the specific
occasion.
In fact, all the route entries must specify
the next hop address. While forwarding a packet, the corresponding route is
determined by searching the routing table for the packet’s destination
address. Only after the next hop address is specified, the corresponding
link-layer address can be found for the link-layer to forward the packet.
3)
Other attributes
You can configure different preferences for
different static routes for the purpose of easy routing management policy. For
example, while configuring multiple routes to the same destination, using
identical preference allows for load sharing while using different preference
allows for routing backup.
S5500-SI series do
not support load sharing.
Before configuring a static route, you need
to finish the following tasks:
l
Configuring the physical parameters for relative
interfaces
l
Configuring the link-layer attribute for
relative interfaces
l
Configuring the IP address for relative
interfaces
Follow these steps to configure a static
route:
|
Operation
|
Command
|
Description
|
|
Enter
system view
|
system-view
|
—
|
|
Configure a
static route
|
ip
route-static ip-address { mask | mask-length
} { [ vlan-interface vlan-id ] nexthop-address | NULL
interface-number } [ preference preference | description
description-info | tag tag-value ]*
|
Required
|
|
Configure the
default preference for a static route
|
ip
route-static default-preference default-preference-value
|
Optional
The preference
is 60 by default.
|
l
While configuring a static route, it will use
the default preference if no value is specified. After resetting the default
preference, it is valid only for the newly created static route.
l
The description text can describe the usage and
function of some specific routes, thus make it easy for you to classify and
manage different static routes.
l
You can easily control the routes by using the
tag set in the routing policy.
l
While running the ip route-static command
to configure static, configuring all-zero destination address and mask
specifies using the default route.
After the configuration, you can run the display
command in any view to display the running status and configuration effect of
the static route configuration.
You can use the delete command in the
system view to delete all the static routes configured.
Follow these steps to display and maintain
a static route:
|
Operation
|
Command
|
|
Display the summary of the IP routing
table
|
display ip routing-table
|
|
Display the details of the IP routing
table
|
display ip routing-table verbose
|
|
Display the information of a static route
|
display ip routing-table protocol
static [ inactive | verbose ]
|
|
Delete all static routes
|
delete static-routes all
|
You can use the undo ip route-static demand in the system view to
delete a static route, and use the delete state-routes all demand in the system
view to delete all the static routes configured (including the default IPv4
routes configured manually) at the same time.
I. Network requirements
The switches’ interfaces and the
hosts’ IP addresses and masks are shown in the following figure. It
requires static routes to connect the hosts for inter-communication.
II. Network diagram
Figure
1-1 Network diagram for static routes
III. Configuration procedure
1)
Configuring the interfaces’ IP addresses
Omitted.
2)
Configuring the static route
# Configure a default route on SwitchA.
<SwitchA> system-view
[SwitchA] ip route-static 0.0.0.0 0.0.0.0
1.1.4.2
# Configure two static routes on SwitchB.
<SwitchB> system-view
[SwitchB] ip route-static 1.1.1.0
255.255.255.0 1.1.4.1
[SwitchB] ip route-static 1.1.3.0
255.255.255.0 1.1.4.6
# Configure a default route on SwitchC.
[Switch B<SwitchC> system-view
[SwitchC] ip route-static 0.0.0.0 0.0.0.0
1.1.4.5
3)
Configure the hosts
The default gateways for the three hosts
PC1, PC2 and PC3 are configured as 1.1.1.1, 1.1.2.1 and 1.1.3.1 respectively.
4)
Display the configuration result
# Display the IP route table of SwitchA.
[SwitchA]display ip routing-table
Routing Tables: Public
Destinations : 7
Routes : 7
Destination/Mask Proto Pre
Cost NextHop Interface
0.0.0.0/0 Static 60
0 1.1.4.2 Vlan100
1.1.1.0/24 Direct 0 0
1.1.1.1 Vlan200
1.1.1.1/32 Direct 0 0
127.0.0.1 InLoop0
1.1.4.0/30 Direct 0 0
1.1.4.1 Vlan100
1.1.4.1/32 Direct 0 0
127.0.0.1 InLoop0
127.0.0.0/8 Direct 0 0
127.0.0.1 InLoop0
127.0.0.1/32 Direct 0 0
127.0.0.1 InLoop0
# Use the ping command to check the
connectivity.
[SwitchA] ping 1.1.3.1
PING 1.1.3.1: 56 data bytes, press
CTRL_C to break
Reply from 1.1.3.1: bytes=56
Sequence=1 ttl=254 time=62 ms
Reply from 1.1.3.1: bytes=56
Sequence=2 ttl=254 time=63 ms
Reply from 1.1.3.1: bytes=56
Sequence=3 ttl=254 time=63 ms
Reply from 1.1.3.1: bytes=56
Sequence=4 ttl=254 time=62 ms
Reply from 1.1.3.1: bytes=56
Sequence=5 ttl=254 time=62 ms
--- 1.1.3.1 ping statistics ---
5 packet(s) transmitted
5 packet(s) received
0.00% packet loss
round-trip min/avg/max = 62/62/63
ms
# Use the tracert command to check
the connectivity.
[SwitchA] tracert 1.1.3.1
traceroute to 1.1.3.1(1.1.3.1) 30
hops max,40 bytes packet, press CTRL_C to break
1 1.1.4.2 31 ms 32 ms 31 ms
2 1.1.4.6 62 ms 63 ms 62 ms
The term "router"
in this document refers to a router in a generic sense or a Layer 3 switch. To
improve readability, this will not be described in the present manual again.
2.1 RIP Overview
RIP is a simple Interior Gateway Protocol
(IGP), which is mainly used in small-size networks, such as academic networks
and simple structured LANs.
RIP is still widely used in practical
networking due to its simple implementation, and easier configuration and maintenance
than OSPF and IS-IS.
I. Basic concept of RIP
RIP is a distance-vector-based routing
protocol, using UDP messages for exchanging information on port 520.
RIP uses a routing metric (Hop Count) to
measure the distance to the destination. The Hop Count value of a router to its
directly connected network is 0. Networks which are reachable through one other
router are one hop etc. To reduce the convergence time, RIP limits the metric
value from 0 to 15. It is considered infinity if the value is equal or larger
than 16, which means the destination network is unreachable. That is why RIP
cannot be used in large scale networks.
RIP prevents routing loops by implementing
Split Horizon and Poison Reverse functions.
II. RIP routing table
Each RIP router has a routing table,
containing routing entries of all reachable destinations.
l
Destination address: the IP address of a host or
a network.
l
Next hop: IP address of the adjacent router to
the destination network.
l
Interface: The interface for forwarding
l
Metric: Cost from the local router to the
destination
l
Routing time: The amount of time since the entry
was last updated. The time is reset to 0 when the routing entry is updated every
time.
l
Route change tag: Indicates that the information
about this route has changed.
III. RIP timers
RIP uses four timers to control its
operation. They are Update, Timeout, Suppress, and Garbage-Collect.
l
Update timer triggers sending new update
messages periodically.
l
Timeout timer controls the validity of a route.
A route is considered as unreachable when the RIP router does not receive
update messages within the aged time from any neighbor.
l
Suppress timer. A route changes to the suppress
status when no updated messages are send within the timeout-value or the
metric value reaches 16. In the suppress status, the router only accepts update
messages with the metric value less than 16 and from the same neighbor to
replace the unreachable route.
l
Garbage-Collect timer. The period from the
metric value of a route reaches 16 to the route is purged from the table is
defined as the garbage collection time in RFC. During the Garbage-Collect time,
RIP keeps advertising the route with a metric value of 16. Once the
Garbage-Collect time expires and the route is not updated, the route is deleted
from the table.
Following procedures describe how RIP
works.
1)
After enabling RIP, the router sends Request
messages to neighboring routers. Neighboring routers return Response messages
including all information about the routing table.
2)
The router updates its local routing table, and
broadcasts the routing updates to its neighbors with triggered updating
messages. All routers on the network do the same to keep the latest routing table.
In RIP, the routing table on each router is
updated upon receipt of RIP messages periodically advertised by neighboring
routers. The aged routes are deleted to make sure routes are always valid. The
procedure is as follows: RIP periodically advertises the local routing table to
neighboring routers, which update their local routes upon receipt of the
packets. This procedure repeats on all RIP-enabled routers.
V. Routing loops prevention
RIP is a D-V based routing protocol. Each
router calculates the distance to a destination based on the routing
information from its neighbors. When a connection to a destination goes down,
there is no way for the router on that connection to notify the others about
its metric changes. The other routers still use the old routing information to
calculate the distance to that destination. Therefore, routing loops can occur
in this case.
RIP uses the following mechanisms to
prevent routing loops.
l
Counting to infinity. The metric value of 16 is
defined as infinity. When a routing loop occurs, the route is considered as
unreachable when the metric value reaches 16.
l
Split Horizon. The router does not send the
routing table to neighboring routers via the same interface on which it
receives. Split Horizon can definitely prevent routing loops and save the
bandwidth.
l
Poison Reverse. The router sends routing tables
through the same interface from which the tables are received with a metric
value of 16 (means infinite). This method can remove useless information in
routing tables of neighboring routers.
l
Triggered Updates. Each router sends out its new
routing table as long as it receives an update, rather than waiting until the
usual update period expires. This can speed up the network convergence.
RIP has two versions: RIP-1 and RIP-2.
RIP-1, a Classful Routing Protocol,
supports broadcasting protocol messages. RIP-1 protocol messages do not carry
mask information, which means it can only recognize routing information on
segments with natural addresses such as Class A, B, and C. That is why RIP-1
does not support routing convergence and Discontiguous Subnet.
RIP-2 is a Classless Routing Protocol.
Compared with RIP-1, RIP-2 has the following advantages.
l
Supports Route Tag. The Route Tag is intended to
differentiate the internal RIP routes from the external RIP routes.
l
Supports masks, route summarization and CIDR
(Classless Inter-Domain Routing).
l
Supports next hop, which must be directly
reachable on the broadcast network.
l
Supports multicasting to reduce unnecessary load
on hosts that do not need to listen to RIP-2 messages.
l
Supports authentication to enhance security.
Plain text authentication and MD5 (Message Digest 5) are two authentication
methods.
RIP-2 has two types
of message transmission: broadcasting and multicasting. Multicasting is the
default type using 224.0.0.9 as the multicast address. The interfaces running
RIP-2 broadcasting can also receive RIP-1 messages.
I. RIP-1 message format
A RIP message consists of Header and Route
Entries which can be up to 25.
The format of RIP-1 message is shown in Figure 2-1.
Figure 2-1 RIP-1 Message Format
l
Command: The type of message. 1 indicates
Request, 2 indicates Response.
l
Version: The version of RIP. RIP-1 is 0x01.
l
AFI (Address Family Identifier): The family of
protocol. 2 is for IP.
l
IP Address: IP address of the destination. Only
natural addresses are acceptable here.
l
Metric: The cost of the route.
II. RIP-2 message format
The format of RIP-2 message is similar with
RIP-1. Figure 2-2 shows it.
Figure 2-2 RIP-2 Message Format
The differences from RIP-1 are stated as
following.
l
Version: The version of RIP. For RIP-2 the value
is 0x02.
l
Route Tag: An attribution to indicate from where
the routes are imported.
l
IP Address: The destination IP address. It could
be a natural address, subnet address or host address.
l
Subnet Mask: Mask of the destination address.
l
Next Hop: The address of the best next hop.
0.0.0.0 indicates that the originator of the route is the best next hop.
III. RIP-2 authentication
RIP-2 supports plain text authentication,
which uses the first Route Entry for authentication. The value of 0xFFFF
indicates that the entry is authentication information rather than routing
information. See Figure 2-3
Figure 2-3 RIP-2 Authentication Message
l
Authentication Type: 2 represents plain text
authentication, while 3 represents MD5.
l
Authentication: The actual authentication data.
It includes the password information when using plain text authentication.
RFC 1723 only
defines plain text authentication. For information about MD5 authentication, see
RFC2082 “RIP-2 MD5 Authentication”.
Currently, S5500-SI Series Ethernet Switches
support the following RIP features.
l
RIP-1
l
RIP-2
l
RFC 1058: Routing Information Protocol
l
RFC 1723: RIP Version 2 - Carrying Additional
Information
l
RFC 1721: RIP Version 2 Protocol Analysis
l
RFC 1722: RIP Version 2 Protocol Applicability
Statement
l
RFC 1724: RIP Version 2 MIB Extension
l
RFC 2082: RIP-2 MD5 Authentication
2.2 RIP Basic Configuration
Before configuring RIP features, please first
configure IP address on each interface, and make sure all routers are
reachable.
Follow these steps to enable RIP:
|
Operation
|
Command
|
Description
|
|
Enter system view
|
system-view
|
––
|
|
Enable RIP and enter RIP view
|
rip [ process-id ]
|
––
|
|
Enable RIP on specified network
|
network network-address
|
Required
Disabled by default
|
l
If you perform some RIP configurations in
interface view before enabling RIP, those configurations will take effect after
RIP is enabled.
l
The router does not send, receive or forward any
routing information if you do not enable RIP on that network.
l
You can enable RIP on all interfaces of the
network by using the network 0.0.0.0 command.
II. Configuring the interface
behavior
Follow these steps to configure interface
behavior:
|
Operation
|
Command
|
Description
|
|
Enter system view
|
system-view
|
––
|
|
Enter RIP view
|
rip [ process-id
]
|
––
|
|
Stop routing updates on interfaces
|
silent-interface { all | interface-type interface-number }
|
Optional
All interfaces can receive routing
updates by default
|
|
Return to system view
|
quit
|
––
|
|
Enter interface view
|
interface interface-type
interface-number
|
––
|
|
Configure an interface to receive routing
updates
|
rip input
|
Optional
By default, the router receives and send RIP
messages
|
|
Configure an interface to send routing
updates
|
rip output
|
Stopping routing updates
means that the router receives routing updates without forwarding them.
III. Configuring the RIP version
Follow these steps to configure the RIP
version:
|
Operation
|
Command
|
Description
|
|
Enter system view
|
system-view
|
––
|
|
Enter RIP view
|
rip [ process-id
]
|
––
|
|
Specify a global RIP version
|
version { 1 | 2 }
|
Optional
RIP-1 by default
|
|
Return to system view
|
quit
|
––
|
|
Enter interface view
|
interface interface-type
interface-number
|
––
|
|
Specify a RIP version on the interface
|
rip version { 1 | 2 [ broadcast | multicast ] }
|
Optional
By default, the router receives RIP-1 and
RIP-2 messages, but only sends RIP-1 messages. If the RIP version is 2, you
can specify the message is broadcast or multicast.
|
If the RIP version specified on the interface and the global RIP
version are inconsistent, the RIP version specified on the interface is used.
If no RIP version is specified on the interface, the global RIP
version is used.
2.3 RIP Route Control
In some complex network environments, you
need to make the RIP configuration more precise.
Before configuring RIP routing information,
finish the following tasks first:
l
Configure IP address on each interface, and make
sure all routers are reachable.
l
Configure basic RIP functions
To increase
the value of routing metrics, you can add a value to the incoming or outgoing
routing metric learned by RIP.
Follow these steps to configure additional
routing metrics:
|
Operation
|
Command
|
Description
|
|
Enter system view
|
system-view
|
––
|
|
Enter interface view
|
interface interface-type
interface-number
|
––
|
|
Define an additional routing metric for
incoming routes
|
rip metricin value
|
Optional
0 by default
|
|
Define an additional routing metric for
outgoing routes
|
rip metricout value
|
Optional
1 by default
|
rip metricout is only applied to its own routing and those learned by RIP. For
those imported from other routing protocols, this command is not applicable.
2.3.2 Configuring route summarization
The route summarization is that subnet
routes in a natural network are summarized until the whole network is
advertised as a single natural mask route. This function can reduce the size of
the routing tables so that to reduce the network load.
RIP-1 does not support route summarization.
So when RIP-2 is running, you need to disable the route summarization function
if you want to advertise all subnet routes.
I. Enable RIP-2 automatic route
summarization
Follow these steps to configure RIP route
summarization:
|
Operation
|
Command
|
Description
|
|
Enter system view
|
system-view
|
––
|
|
Enter RIP view
|
rip [ process-id
]
|
––
|
|
Enable RIP-2 automatic route
summarization
|
summary
|
Optional
Enabled by default
|
II.
Assign a summary IP address
Follow these steps to assign a summary IP
address:
|
Operation
|
Command
|
Description
|
|
Enter system view
|
system-view
|
––
|
|
Enter RIP view
|
rip [ process-id
]
|
––
|
|
Disable RIP-2 automatic route
summarization
|
undo summary
|
Optional
Enabled by default
|
|
Return to system view
|
quit
|
––
|
|
Enter interface view
|
interface interface-type
interface-number
|
––
|
|
Assign an IP address and network mask for
the summarized routes to be advertised
|
rip summary-address ip-address network-{ mask | mask-length
}
|
Optional
|
In some cases, the router can get lots of
routing information from the same network hosts, which are not helpful for
routing but taking large of the network resources. After disabling the host
route function, the router discards the host route information.
Follow these steps to configure host route:
|
Operation
|
Command
|
Description
|
|
Enter system view
|
system-view
|
––
|
|
Enter RIP view
|
rip [ process-id
]
|
––
|
|
Disabling the receiving of host routes
|
undo host-route
|
Optional
Enabled by default
|
2.3.4 Configuring default route
Follow these steps to configure RIP default
route:
|
Operation
|
Command
|
Description
|
|
Enter system view
|
system-view
|
––
|
|
Enter RIP view
|
rip [ process-id
]
|
––
|
|
Configure a RIP default route
|
default-route originate cost value
|
Required
|
2.3.5 Configuring route filtering
Route filtering is supported by the router.
You can filter incoming and outgoing routes by setting the inbound and outbound
filter policies in the access list and IP address prefixes list. You can also
specify the incoming routes from particular neighbors.
Follow these steps to configure route
filtering:
|
Operation
|
Command
|
Description
|
|
Enter system view
|
system-view
|
––
|
|
Enter RIP view
|
rip [ process-id
]
|
––
|
|
Define the filtering policy
|
filter-policy { acl-number | [ ip-prefix ip-prefix-name ][
gateway ip-prefix-name ] | gateway ip-prefix-name
} import [ interface-type interface-number ]
|
Required
|
|
Define the filtering policy for the
redistributed route
|
