When configuring a static route, go to
these sections for information you are interested in:
l
Introduction
l
Configuring
a Static Route
l
Detecting
Reachability of the Static Route’s Nexthop
l
Displaying
and Maintaining Static Routes
l
Configuration
Example
The term
“router” in this document refers to a router in a generic sense or
a Layer 3 switch.
1.1 Introduction
A static route is a special route that is manually
configured by the network administrator. If a network’s topology is
simple, you only need to configure static routes for the network to work
normally. The proper configuration and usage of static routes can improve
network performance and ensure bandwidth for important network applications.
The
disadvantage of using static routes is that they cannot adapt to network
topology changes. If a fault or a topological change occurs in the network, the
routes will be unreachable and the network breaks. In this case, the network
administrator has to modify the static routes manually.
A router selects the default route only
when it cannot find any matching entry in the routing table.
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 fails to match any entry in the routing
table, the packet will be discarded and an ICMP packet will be sent to the
source to report that the destination or the network is unreachable.
You can create the default route with both
destination and mask being 0.0.0.0, and some dynamic routing protocols, such as
OSPF, RIP and IS-IS, can also generate the default route.
Before configuring a static route, you need
to know the following concepts:
1)
Destination address and mask
In the ip route-static command, an
IPv4 address is in dotted decimal format and a mask can be either in dotted
decimal format or in the form of mask length (the digits of consecutive 1s in
the mask).
2)
Output interface and next hop address
While configuring a static route, you can
specify either the output interface or the next hop address depending on the
specific occasion. The next hop address can not be a local interface IP
address; otherwise, the route configuration will not take effect.
In fact, all the route entries must have a
next hop address. When forwarding a packet, a router first searches the routing
table for the route to the destination address of the packet. The system can
find the corresponding link layer address and forward the packet only after the
next hop address is specified.
When specifying the output interface, note
that:
l
If the output interface is a NULL 0 interface,
there is no need to configure the next hop address.
l
You are not recommended to specify a broadcast
interface (such as VLAN interface) as the output interface, because a broadcast
interface may have multiple next hops. If you have to do so, you must specify
the corresponding next hop for the output interface.
3)
Other attributes
You can configure different preferences for
different static routes so that route management policies can be applied more
flexibly. For example, specifying the same preference for different routes to
the same destination enables load sharing, while specifying different
preferences for these routes enables route backup.
1.2 Configuring a Static Route
Before configuring a static route, you need
to configure the IP addresses for related interfaces.
Follow these steps to configure a static
route:
|
To do…
|
Use the command…
|
Remarks
|
|
Enter system view
|
system-view
|
—
|
|
Configure a static route
|
ip route-static
dest-address { mask | mask-length } { next-hop-address
| interface-type interface-number [ next-hop-address ] }
[ preference preference-value ] [ tag tag-value ]
[ description description-text ]
|
Required
By default, preference for static
routes is 60, tag is 0, and no description information is configured.
|
|
Configure the default preference for
static routes
|
ip route-static default-preference default-preference-value
|
Optional
60 by default
|
l
When configuring a static route, the static
route does not take effect if you specify the next hop address first and then
configure it as the IP address of a local interface, such as a VLAN interface.
l
If you do not specify the preference when
configuring a static route, the default preference will be used. Reconfiguring
the default preference applies only to newly created static routes.
l
You can flexibly control static routes by
configuring tag values and using the tag values in the routing policy.
l
If the destination IP address and mask are both
configured as 0.0.0.0 with the ip route-static command, the route is the
default route.
1.3 Detecting Reachability of the Static
Route’s Nexthop
If a static route fails due to a topology
change or a fault, the connection will be interrupted. To improve network
stability, the system needs to detect reachability of the static route’s
next hop and switch to a backup route once the next hop is unreachable.
If you specify the nexthop but not outgoing
interface when configuring a static route, you can associate the static route
with a track entry to check the static route validity:
l
When the track entry is positive, the static
route's nexthop is reachable and the static route takes effect.
l
When the track entry is negative, the static
route's nexthop is unreachable and the static route is invalid. For details
about track, refer to Track Configuration.
I. Network requirements
To detect the reachability of a static
route's nexthop through a Track entry, you need to create a Track first. For
detailed Track configuration procedure, refer to Track Configuration.
Follow these steps to detect the
reachability of a static route's nexthop through Track:
|
To do…
|
Use the command…
|
Remarks
|
|
Enter system view
|
system-view
|
—
|
|
Associate the static route with a track
entry
|
ip route-static dest-address { mask | mask-length
} next-hop-address track track-entry-number [
preference preference-value ] [ tag tag-value ] [
description description-text ]
|
Required
Not configured by default
|
l
To configure this feature for an existing static
route, simply associate the static route with a track entry. For a non-existent
static route, configure it and associate it with a Track entry.
l
If a static route needs route recursion, the
associated track entry must monitor the nexthop of the recursive route instead
of that of the static route; otherwise, a valid route may be mistakenly
considered invalid.
|
To do…
|
Use the command…
|
Remarks
|
|
Display the current configuration
information
|
display current-configuration
|
Available in any view
|
|
Display the brief information of the IP
routing table
|
display ip routing-table
|
|
Display the detailed information of the
IP routing table
|
display ip routing-table verbose
|
|
View information of static routes
|
display ip routing-table protocol static [ inactive | verbose
]
|
|
Delete all the static routes
|
delete static-routes all
|
Available In system view
|
1.5 Configuration Example
I. Network requirements
The IP addresses and masks of the switches
and hosts are shown in the following figure. Static routes are required for
interconnection between any two hosts.
II. Network diagram
Figure
1-1 Network diagram for static route configuration
III. Configuration procedure
1)
Configuring IP addresses for interfaces
(omitted)
2)
Configuring static routes
# Configure a default route on Switch A
<SwitchA> system-view
[SwitchA] ip route-static 0.0.0.0
0.0.0.0 1.1.4.2
# Configure two static routes on Switch B
<SwitchB> system-view
[SwitchB] ip route-static 1.1.2.0
255.255.255.0 1.1.4.1
[SwitchB] ip route-static 1.1.3.0
255.255.255.0 1.1.5.6
# Configure a default route on Switch C
<SwitchC> system-view
[SwitchC] ip route-static 0.0.0.0
0.0.0.0 1.1.5.5
3)
Configure the hosts
The default gateways for the three hosts A,
B and C are 1.1.2.3, 1.1.6.1 and 1.1.3.1 respectively. The configuration
procedure is omitted.
4)
Display the configuration result
# Display the IP routing table of Switch A.
[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 Vlan500
1.1.2.0/24 Direct 0
0 1.1.2.3 Vlan300
1.1.2.3/32 Direct 0
0 127.0.0.1 InLoop0
1.1.4.0/30 Direct 0
0 1.1.4.1 Vlan500
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
# Display the IP routing table of Switch B.
[SwitchB] display ip routing-table
Routing Tables: Public
Destinations : 10
Routes : 10
Destination/Mask Proto Pre
Cost NextHop Interface
1.1.2.0/24 Static 60
0 1.1.4.1 Vlan500
1.1.3.0/24 Static 60
0 1.1.5.6 Vlan600
1.1.4.0/30 Direct 0
0 1.1.4.2 Vlan500
1.1.4.2/32 Direct 0
0 127.0.0.1 InLoop0
1.1.5.0/30 Direct 0
0 1.1.5.5 Vlan600
1.1.5.5/32 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
1.1.6.0/24 Direct 0
0 1.1.6.1 Vlan100
1.1.6.1/32 Direct 0
0 127.0.0.1 InLoop0
# From Host A, use the ping command
to verify the network layer reachability to Host B and Host C.
l
The term “router” in this document
refers to a router in a generic sense or a Layer 3 switch.
l
The S5500-SI series only support single RIP
process.
When configuring RIP, go to these sections
for information you are interested in:
l
RIP Overview
l
Configuring RIP Basic
Functions
l
Configuring RIP Route
Control
l
Configuring RIP Network
Optimization
l
Displaying and Maintaining
RIP
l
RIP Configuration
Examples
l
Troubleshooting RIP
2.1 RIP Overview
RIP is a simple Interior Gateway Protocol
(IGP), mainly used in small-sized networks, such as academic networks and
simple LANs. RIP is not applicable to complex networks.
RIP is still widely used in practical
networking due to easier implementation, configuration and maintenance than
OSPF and IS-IS.
I. Basic concepts
RIP is a distance vector routing protocol,
using UDP packets for exchanging information through port 520.
RIP uses a hop count to measure the
distance to a destination. The hop count is known as the metric. The hop count
from a router to a directly connected network is 0. The hop count from one
router to a directly connected router is 1. To limit convergence time, the
range of RIP metric value is from 0 to 15. A metric value of 16 (or bigger) is
considered infinite, which means the destination network is unreachable. That
is why RIP is not suitable for large-scaled networks.
RIP prevents routing loops by implementing
the split horizon and poison reverse functions.
II. RIP routing table
A RIP router has a routing table containing
routing entries of all reachable destinations, and each routing entry contains:
l
Destination address: IP address of a host or a
network.
l
Next hop: IP address of the adjacent
router’s interface to reach the destination.
l
Egress interface: Packet outgoing interface.
l
Metric: Cost from the local router to the
destination.
l
Route time: Time elapsed since the routing entry
was last updated. The time is reset to 0 every time the routing entry is
updated.
l
Route tag: Identifies a route, used in a routing
policy to flexibly control routes. For information about routing policy, refer
to Routing Policy Configuration.
RIP employs four timers, update, timeout,
suppress, and garbage-collect.
l
The update timer defines the interval between
routing updates.
l
The timeout timer defines the route aging time.
If no update for a route is received within the aging time, the metric of the
route is set to 16 in the routing table.
l
The suppress timer defines how long a RIP route
stays in the suppressed state. When the metric of a route is 16, the route
enters the suppressed state. In the suppressed state, only routes which come
from the same neighbor and whose metric is less than 16 will be received by the
router to replace unreachable routes.
l
The garbage-collect timer defines the interval
from when the metric of a route becomes 16 to when it is deleted from the
routing table. During the garbage-collect timer length, RIP advertises the
route with the routing metric set to 16. If no update is announced for that
route after the garbage-collect timer expires, the route will be deleted from
the routing table.
IV. Routing loops prevention
RIP is a distance vector (D-V) routing protocol.
Since a RIP router advertises its own routing table to neighbors, routing loops
may occur.
RIP uses the following mechanisms to
prevent routing loops.
l
Counting to infinity. The metric value of 16 is
defined as unreachable. When a routing loop occurs, the metric value of the
route will increment to 16.
l
Split horizon. A router does not send the
routing information learned from a neighbor to the neighbor to prevent routing
loops and save bandwidth.
l
Poison reverse. A router sets the metric of
routes received from a neighbor to 16 and sends back these routes to the
neighbor to help delete useless information from the neighbor’s routing
table.
l
Triggered updates. A router advertises updates
once the metric of a route is changed rather than after the update period
expires to speed up network convergence.
The following procedure describes how RIP
works.
1)
After RIP is enabled, the router sends Request
messages to neighboring routers. Neighboring routers return Response messages
including information about their routing tables.
2)
After receiving such information, the router
updates its local routing table, and sends triggered update messages to its
neighbors. All routers on the network do the same to keep the latest routing
information.
3)
By default, a RIP router sends its routing table
to neighbors every 30 seconds.
4)
RIP ages out routes by adopting an aging
mechanism to keep only valid routes.
RIP has two versions, RIPv1 and RIPv2.
RIPv1, a classful routing protocol,
supports message advertisement via broadcast only. RIPv1 protocol messages do
not carry mask information, which means it can only recognize routing
information of natural networks such as Class A, B, C. That is why RIPv1 does
not support discontiguous subnets.
RIPv2 is a classless routing protocol.
Compared with RIPv1, RIPv2 has the following advantages.
l
Supporting route tags. Route tags are used in
routing policies to flexibly control routes.
l
Supporting masks, route summarization and
Classless Inter-Domain Routing (CIDR).
l
Supporting designated next hops to select the
best next hops on broadcast networks.
l
Supporting multicast routing update to reduce
resource consumption.
l
Supporting plain text authentication and MD5
authentication to enhance security.
RIPv2 has two types
of message transmission: broadcast and multicast. Multicast is the default type
using 224.0.0.9 as the multicast address. The interface working in the RIPv2
broadcast mode can also receive RIPv1 messages.
I. RIPv1 message format
A RIPv1 message consists of a header and up
to 25 route entries.
Figure 2-1 shows the
format of RIPv1 message.
Figure 2-1 RIPv1 Message Format
l
Command: Type of message. 1 indicates request,
and 2 indicates response.
l
Version: Version of RIP, 0x01 for RIPv1.
l
AFI: Address Family Identifier, 2 for IP.
l
IP Address: Destination IP address of the route.
It can be a natural network, subnet or a host address.
l
Metric: Cost of the route.
II. RIPv2 message format
The format of RIPv2 message is similar with
RIPv1. Figure 2-2
shows it.
Figure 2-2 RIPv2 Message Format
The differences from RIPv1 are stated as
following.
l
Version: Version of RIP. For RIPv2 the value is
0x02.
l
Route Tag: Route Tag.
l
IP Address: Destination IP address. It could be
a natural network address, subnet address or host address.
l
Subnet Mask: Mask of the destination address.
l
Next Hop: If set to 0.0.0.0, it indicates that
the originator of the route is the best next hop; otherwise it indicates a next
hop better than the originator of the route.
III. RIPv2 authentication
RIPv2 sets the AFI field of the first route
entry to 0xFFFF to identify authentication information. See Figure 2-3.
Figure 2-3 RIPv2 Authentication Message
l
Authentication Type: 2 represents plain text
authentication, while 3 represents MD5.
l
Authentication: Authentication data, including
password information when plain text authentication is adopted or including key
ID, MD5 authentication data length and sequence number when MD5 authentication
is adopted.
l
RFC 1723 only defines plain text authentication.
For information about MD5 authentication, refer to RFC2082 “RIPv2 MD5
Authentication”.
l
With RIPv1, you can configure the authentication
mode in interface view. However, the configuration will not take effect because
RIPv1 does not support authentication.
The current implementation supports RIPv1
and RIPv2
RFC 1058: Routing Information Protocol
RFC 1723: RIP Version 2 - Carrying
Additional Information
RFC 1721: RIP Version 2 Protocol Analysis
RFC 1722: RIP Version 2 Protocol
Applicability Statement
RFC 1724: RIP Version 2 MIB Extension
RFC 2082: RIPv2 MD5 Authentication
2.2 Configuring RIP Basic Functions
Before configuring RIP basic functions,
configure IP addresses for interfaces, making all adjacent nodes reachable to
each other at the network layer.
Follow these steps to enable RIP:
|
To do…
|
Use the command…
|
Remarks
|
|
Enter system view
|
System-view
|
––
|
|
Enable a RIP process and enter RIP view
|
rip [ process-id ]
|
Required
Not
enabled by default
|
|
Enable RIP on the interface attached to
the specified network
|
network network-address
|
Required
Disabled
by default
|
l
If you make some RIP configurations in interface
view before enabling RIP, those configurations will take effect after RIP is
enabled.
l
RIP runs only on the interfaces residing on the
specified networks. Therefore, you need to specify the network after enabling
RIP to validate RIP on a specific interface.
l
You can enable RIP on all interfaces using the
command network 0.0.0.0.
II. Configuring the interface
behavior
Follow these steps to configure the
interface behavior:
|
To do…
|
Use the command…
|
Remarks
|
|
Enter system view
|
system-view
|
––
|
|
Enter RIP view
|
rip [ process-id
]
|
––
|
|
Disable an or all interfaces from sending
routing updates (the interfaces can still receive updates)
|
silent-interface { all | interface-type interface-number }
|
Optional
All interfaces can send routing updates
by default.
|
|
Return to system view
|
quit
|
—
|
|
Enter interface view
|
interface interface-type
interface-number
|
—
|
|
Enable the interface to receive RIP
messages
|
rip input
|
Optional
Enabled by default
|
|
Enable the interface to send RIP messages
|
rip output
|
Optional
Enabled by default
|
III. Configuring a RIP version
You can configure a RIP version in RIP or
interface view.
l
If neither global nor interface RIP version is
configured, the interface sends RIPv1 broadcasts and can receive RIPv1
broadcast and unicast packets, and RIPv2 broadcast, multicast, and unicast
packets.
l
If an interface has no RIP version configured,
it uses the global RIP version; otherwise it uses the RIP version configured on
it.
l
With RIPv1 configured, an interface sends RIPv1
broadcasts, and can receive RIPv1 broadcasts and RIPv1 unicasts.
l
With RIPv2 configured, a multicast interface
sends RIPv2 multicasts and can receive RIPv2 unicasts, broadcasts and
multicasts.
l
With RIPv2 configured, a broadcast interface
sends RIPv2 broadcasts and can receive RIPv1 unicasts, and broadcasts, and
RIPv2 broadcasts, multicasts and unicasts.
Follow these steps to configure a RIP
version:
|
To do…
|
Use the command…
|
Remarks
|
|
Enter system view
|
system-view
|
––
|
|
Enter RIP view
|
rip [ process-id
]
|
––
|
|
Specify a global RIP version
|
version { 1 | 2 }
|
Optional
By
default, if an interface has a RIP version specified, the version takes
precedence over the global one. If no RIP version is specified for an
interface, the interface can send RIPv1 broadcasts, and receive RIPv1
broadcasts, unicasts, RIPv2 broadcasts, multicasts and unicasts.
|
|
Return to system view
|
Quit
|
—
|
|
Enter interface view
|
interface interface-type
interface-number
|
––
|
|
Specify a RIP version for the interface
|
rip
version { 1 | 2 [ broadcast
| multicast ] }
|
Optional
|
In complex networks, you need to configure
advanced RIP features.
This section covers the following topics:
l
Configuring
an Additional Routing Metric
l
Configuring
RIPv2 Route Summarization
l
Disabling
Host Route Reception
l
Advertising
a Default Route
l
Configuring
Inbound/Outbound Route Filtering
l
Configuring
a Priority for RIP
l
Configuring
RIP Route Redistribution
Before configuring RIP routing feature,
complete the following tasks:
l
Configure an IP address for each interface, and
make sure all neighboring routers are reachable to each other.
l
Configure RIP basic functions
2.3.1 Configuring an Additional Routing Metric
An additional routing metric can be added
to the metric of an inbound or outbound RIP route.
The outbound additional metric is added to
the metric of a sent route, the route’s metric in the routing table is
not changed.
The inbound additional metric is added to
the metric of a received route before the route is added into the routing
table, so the route’s metric is changed.
Follow these steps to configure additional
routing metrics:
|
To do…
|
Use the command…
|
Remarks
|
|
Enter system view
|
system-view
|
––
|
|
Enter interface view
|
interface interface-type
interface-number
|
––
|
|
Define an inbound additional routing
metric
|
rip metricin [ route-policy route-policy-name ] value
|
Optional
0 by default
|
|
Define an outbound additional routing
metric
|
rip metricout [ route-policy route-policy-name ] value
|
Optional
1 by default
|
2.3.2 Configuring RIPv2 Route Summarization
Route summar
