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AR Router Maintenance Guide-FAQ(IP Routing)

Latest reply: Apr 12, 2018 15:04:57 2051 2 0 0 1

2.8  IP Routing

2.8.1  After Configuring the IP Address on a Sub-Interface, Why Can I Not Ping the Sub-Interface?

You have to run arp broadcast enable on the sub-interface to be able to ping the sub-interface.

2.8.2  What Are Rules for Route Selection?

  • Rule 1: The route with higher priority is preferred. A small value indicates a high priority. If a route cannot be selected using this rule, go to rule 2.

  • Rule 2: If two routes have the same priority, the route with the higher internal protocol preference is preferred. A small value indicates a high priority. If a route cannot be selected using this rule, go to rule 3.

  • Rule 3: If two routes have the same priority and belong to the same protocol, the route with the lower-cost value is preferred. If the cost values of two routes are the same, load balancing can be formed. If the number of routes for forming load balancing exceeds the maximum value (such as m) set by the system, the total number of only the first m routes act as the active routes.

2.8.3  After I Run the display fib Command, What Does Flag Mean in the Command Output?

Currently, Flag can have the following values:

  • B: a blackhole route, that is, a route with the outbound interface NULL0.

  • D: a route generated by a dynamic routing protocol such as Intermediate System to Intermediate System routing protocol (IS-IS), open shortest path first (OSPF), Border Gateway Protocol (BGP), or Routing Information Protocol (RIP).

  • G: a gateway route, that is, a route with a gateway as the destination address.

  • H: a host route.

  • S: a static route, that is, a route configured using the ip route-static command or configured on the network management system (NMS).

  • U: a route that is reachable.

2.8.4  What Is the Maximum Number of Paths That AR Series Routers Support to Perform Load Balancing?

The AR100&AR120&AR150&AR160&AR200&AR1200 series, AR2201-48FE, AR2202-48FE, AR2204-27GE, AR2204-27GE-P, AR2204-24GE, AR2204-51GE-P, AR2204-51GE, AR2204-51GE-R, AR2204-48GE-P, AR2204E, AR2204E-D, and AR2204 support a maximum of four paths. AR2220, AR2240, and AR3200 series support a maximum of eight paths.

6711c418de1945a6a6d6c41745fe9374 NOTE:

In V200R005C10 and later versions, devices with SRU200 or SRU400 installed support a maximum of 16 next hops for load balancing.

In V200R006 and later versions, devices with SRUX5 or SRU400 installed support a maximum of 16 next hops for load balancing.

In V200R007 and later versions, devices with SRU200E installed support a maximum of 16 next hops for load balancing.

2.8.5  How Can I Configure Valid Static Routes?

Only when the outbound interface is in Up state, you can run the display ip routing-table command to query routing information in dynamic and static routing entries. If the outbound interface is not in Up state, the route is deactivated. You can run the display ip routing-table protocol command to check whether a route is activated.

2.8.6  Is the Static Route Affected If the BFD for the Static Route is in AdminDown State?

The static route is not affected. The static route is invalid only when the BFD detects a link fault.

2.8.7  What Are the Requirements for the Static Route that Is Associated with an NQA?

The destination address of an NQA test instance cannot be the destination address of an associated static route.

2.8.8  Why Are Neighbors Not Displayed After RIP IS Configured?

This is due to the IP Operating System (IPOS) implementation. Verify that the Routing Information Protocol (RIP) imported the route, and view the RIP neighbors again.

2.8.9  What Advantages Does RIP-2 Have Compared with RIP-1?

  • Routing Information Protocol version 2 (RIP-2) supports the tagging of external routes and uses the routing policy to flexibly control routes based on the tag.

  • RIP-2 packets contain mask information and support route aggregation and Classless Inter-domain Routing (CIDR).

  • RIP-2 supports specifying the next hop so that the optimal next-hop address can be specified on the broadcast network.

  • RIP-2 supports sending update packets for multicast routes. Only devices that support RIP-2 can receive RIP-2 packets. This reduces resource consumption.

  • RIP-2 provides two packet authentication modes, namely, plain text authentication and message digest algorithm 5 (MD5) authentication, to enhance security.

2.8.10  What Are Differences Between the Default Version of RIP, RIP Version 1, and RIP Version 2?

  • Default version: The protocol stack can receive Routing Information Protocol (RIP) version 1 and RIP version 2 packets, but can send only RIP version 1 packets.

  • Version 1: The protocol stack can send and receive only RIP version 1 packets.

  • Version 2: The protocol stack can receive RIP version 1 and RIP version 2 packets, but can send only RIP version 2 packets.

2.8.11  How Do I Change the Priority of a RIP Route?

Because RIP packets cannot carry the preference field, the router priority is valid only for local RIP routes.

To change the priority of a RIP route, run the preference { preference | route-policy route-policy-name }* command in the RIP view of the receiver. You can also apply a routing policy to set a priority for a specific route.

2.8.12  How Do I Calculate the Cost of an IGP Route?

IGP protocols include RIP, IS-IS, and OSPF.

Calculating the Cost of a RIP Route

RIP measures the distance from the local end to the destination by hop count. The hop count is also called the metric. RIP defines that the hop count from a router to a directly connected network is 0, and the hop count from a router to a network that can be reached through another router is 1. The hop count increases with the number of routers between the local router and the destination network. To limit the convergence time, RIP defines that the hop count must be an integer ranging from 0 to 15. A hop count of 16 or greater is defined as infinite. That is, the destination network or host is unreachable.

An interface does not add the cost to RIP routes to be sent, but increases the cost by 1 for the received RIP routes. You can run the following commands to change the cost of routes:
  • After you run the rip metricin command, the AR100&AR120&AR150&AR160&AR200&AR1200&AR2200&AR3200&AR3600 adds an additional metric to a received route, and then adds the route to the routing table. Then the metric of the route changes in the routing table. This command affects route selection on the local device and other devices.
  • After you run the rip metricout command, the AR100&AR120&AR150&AR160&AR200&AR1200&AR2200&AR3200&AR3600 adds an additional metric to a route when advertising the route. The metric of the route, however, does not change in the routing table. This command does not affect route selection on the local device, but affects route selection on other devices.
6711c418de1945a6a6d6c41745fe9374 NOTE:
You can run one of the following commands to set the metric of the imported routes. The following commands are listed in descending order of priority:
  • Run the apply cost command to set the route cost.
  • Run the import-route (RIP) command to set the cost for imported routes.
  • Run the default-cost (RIP) command to set the cost for default routes.

Calculating the Cost of an IS-IS Route

On an IS-IS network, the default cost of an IS-IS interface is 10. The cost of an IS-IS route is the sum of costs of all links between the source device and the destination device.

The link cost of an IS-IS interface can be calculated in the following modes in descending order of priority:
  • Run the isis cost command to set the link cost for a specified IS-IS interface.

  • Run the circuit-cost command to set the link cost for all IS-IS interfaces.

  • Run the auto-cost enable command to enable automatic calculation of the link cost of an interface.

    Before using the auto-cost enable command, run the bandwidth-reference command to set the bandwidth reference value. By default, the bandwidth reference value is 100 Mbit/s. The bandwidth reference value takes effect only when the cost type is wide or wide-compatible. The cost of each interface is calculated as follows:
    • Cost of each interface = (Bandwidth reference value/Interface bandwidth) x 10
    If the cost type is narrow, narrow-compatible, or compatible, the cost of each interface can be obtained from Table 2-39.
    Table 2-39  Relationship between the IS-IS interface cost and interface bandwidth

    Cost

    Bandwidth Range

    60

    Interface bandwidth ≤ 10 Mbit/s

    50

    10 Mbit/s < interface bandwidth ≤ 100 Mbit/s

    40

    100 Mbit/s < interface bandwidth ≤ 155Mbit/s

    30

    155 Mbit/s < interface bandwidth ≤ 622 Mbit/s

    20

    622 Mbit/s < Interface bandwidth ≤ 2.5 Gbit/s

    10

    Interface bandwidth > 2.5 Gbit/s

6711c418de1945a6a6d6c41745fe9374 NOTE:

A Level-1 router in the Level-1 area must communicate with a router outside the Level-1 area through the default route generated on the Level-1-2 router. Therefore, the cost of the route from the Level-1 router to the router outside the Level-1 area is the cost of the route from the Level-1 router to the closest Level-1-2 router.

IS-IS can be configured to specify the cost for the imported route or retain the original cost of the imported route.

Calculating the Cost of the OSPF Route

Similar to the cost of an IS-IS route, the cost of an OSPF route is the sum of costs of all links along the route. By default, the link cost of an OSPF interface is 1.

You can run the ospf cost command to set the cost for a specified OSPF interface. If no interface cost is configured, the system calculates the interface cost using the following formula:
  • Cost of each interface = Bandwidth reference value/Interface bandwidth
The integer portion of the calculation result is taken as the cost of the interface. If the value is smaller than 1, OSPF takes 1 as the interface cost. By default, the bandwidth reference value is 100 Mbit/s. You can change the cost of an OSPF interface by running the bandwidth-reference command to change the bandwidth reference value.
6711c418de1945a6a6d6c41745fe9374 NOTE:

Packets between the stub router or total stub router and a router outside the AS are forwarded through the default route generated on the ABR. Therefore, the cost of the route from the stub router or total stub router to the router outside the AS is the cost of the route from the outside the stub router or total stub router to the closest ABR. Similarly, the cost of the route from the NSSA router to a router in another area or AS is the cost of the route from the NSSA router to the closest ABR or ASBR.

2.8.13  Do I Have to Ensure That Interfaces on the Two Ends of the Link Are on the Same Segment and Have the Same Masks During the Establishment of the OSPF Neighbor Relationship?

The interfaces on the broadcast network, Non-Broadcast Multi-Access (NBMA) network, and point-to-multipoint (P2MP) network must be on the same network segment and the mask digits on the neighboring interfaces must be consistent. The point-to-point (P2P) network does not have this restriction.

2.8.14  Why Can I Not Establish the OSPF Neighbor Relationship over ATM or FR Links?

The possible cause of this is that the IP address of the neighboring router and designated router (DR) priority are not configured.

2.8.15  Can OSPF Import IBGP Routes?

In V200R001C00, open shortest path first (OSPF) cannot import Internal Border Gateway Protocol (IBGP) routes.

Starting from V200R001C01, the OSPF protocol can import IBGP routes. By default, the OSPF protocol does not import IBGP routes.

However, OSPF can import IBGP routes on Multi-VPN-Instance CE (MCE) devices. You can run the vpn-instance-capability simple command for OSPF processes to disable route loop detection and directly calculate routes.

2.8.16  Which OSPF Interfaces Require Peers?

You must configure peers on interfaces in the open shortest path first (OSPF) view, if the link type of the network is Non-Broadcast Multi-Access (NBMA).

2.8.17  Why Cannot Interfaces of Different Types Generate Equal-Cost Routes and Establish OSPF Load Balancing?

OSPF can automatically calculate the cost of an interface based on the interface bandwidth. The calculation formula is: Interface cost = Bandwidth reference value/Interface bandwidth. The bandwidth reference value is configurable. The default value is 100 Mbit/s. Routes generated by OSPF have the same priority (10 by default). The interface cost, however, depends on the interface type. Interfaces of different types have different costs; therefore, the interfaces cannot generate equal-cost routes, leading to failure in establishing load balancing.

2.8.18  How Can I Set the cost Value When OSPF Imports External Routes?

When OSPF imports external routes, the cost of original routes is not used. By default, the cost of the external routes imported by OSPF is 1.

To change the default cost value of external routes imported by OSPF, run the default { cost { cost | inherit-metric } command. In the preceding command:
  • cost: specifies the cost of the imported external routes. The value is an integer ranging from 0 to 16777214.
  • inherit-metric: indicates that the cost of the imported external routes is the cost carried in the route.

2.8.19  What Are the Rules for Selecting Routes Belonging to Different OSPF Processes?

OSPF supports multi-processes. Multiple OSPF processes can run on the same router independently.

Assume that a router is configured with two OSPF processes: process 1 and process 2. They are independent of each other. Therefore, both of the routes belonging to process 1 and process 2 are advertised to the routing management (RM) module. Route selection between the two processes complies with the following rules:
  1. The RM module checks the protocol preference of process 1 and process 2. The route belonging to the process with higher protocol preference is selected as the optimal route.
    6711c418de1945a6a6d6c41745fe9374 NOTE:

    To set the preference of an OSPF route in the specified process, run the preference [ ase ] { preference | route-policy route-policy-name } * command. The default preference of an OSPF route is 10. When an ASE is specified, the default value is 150.

  2. When the protocol preferences of the two processes are the same, the RM module compare the cost of the two routes. The route with smaller cost value is selected as the optimal route.
    6711c418de1945a6a6d6c41745fe9374 NOTE:

    When selecting the optimal route, the RM module first compares the protocol preference. The RM module compares the cost of routes only when the protocol preferences are the same.

2.8.20  Why the Number of Routes in the OSPF Routing Table of the OSPF VPN Multi-instance Is Less than the Predicted Number?

In the OSPF VPN multi-instance, loops may occur if PEs and CEs learn BGP and OSPF routes from each other. You can set the DN in Type3, Type5, or Type7 LSAs advertised by PEs to 1 so that CEs ignore the LSAs with the DN value of 1. These LSAs are not used in route calculation, which prevents loops.

If the preceding method is used to prevent loops, the number of routes in the OSPF routing table is less than the predicted number. To use the LSAs with DN 1 in route calculation, run the vpn-instance-capability simple command on CEs to disable routing loop detection.

2.8.21  When Configured with a Link State Protocol, Why Can the Local Device Not Establish Neighbor Relationship with the Peer Device?

When the local device is configured with a link state protocol, first check the type of the interface on the peer device.
  • To set the network type for an OSPF interface, run the ospf network-type command.
  • To set the network type of an IS-IS interface to P2P, run the isis circuit-type p2p command.

The network types of the interfaces on both ends of a link must be the same; otherwise, the neighbor relationship cannot be established.

2.8.22  Why Can IS-IS Neighbors Not Be Established?

This has the following possible causes:

  • Point-to-multipoint (P2MP) interfaces do not support the Intermediate System to Intermediate System routing protocol (IS-IS).

  • The MTU of the Ethernet Interface is smaller than the max-size of IS-IS LSP packets plus 3.

  • The MTU of the point-to-point (P2P) interface is less than the length of the IS-IS LSP packet.

  • The two ends have different parameter configurations.

2.8.23  Why Does the IS-IS Neighbor Relationship Fail to Be Established on the DSLAM?

Figure 2-10 shows the actual networking.

Figure 2-10  Networking
7101afd43ed34cfca461022e62510ef6

IS-IS transmits BPDU packets whose MAC address is in 0180-C2##-####-#### format. BPDU packets are reserved multicast packets at the link layer and need to carry VLAN tags when transparently transmitted by the DSLAM. IS-IS Hello packets do not carry VLAN tags when being transmitted through Layer 3 GE interfaces; therefore, the DSLAM fails to transparently transmit IS-IS Hello packets. The PON interface receives no IS-IS Hello packet from the peer end, so the PON interface fails to establish the neighbor relationship.

To address this problem, configure the GE interface as a subinterface which allows packets to carry VLAN tags so that the DSLAM can transparently transmit these packets.

6711c418de1945a6a6d6c41745fe9374 NOTE:
The DSLAM adds VLAN tags to packets sent by a PON interface.

2.8.24  Which Networks Are the IS-IS and OSPF Deployed On?

The Intermediate System to Intermediate System routing protocol (IS-IS) is deployed on backbone networks. The open shortest path first (OSPF) is deployed on metropolitan area networks (MANs).

2.8.25  Do PPP Links Support the IS-IS Routing Protocol?

Yes.

2.8.26  What Is the Function of BGP MD5 Authentication, and What Are the Functions of the simple Parameter and the cipher Parameter?

Border Gateway Protocol (BGP) message digest algorithm 5 (MD5) authentication sets MD5 authentication passwords for Transmission Control Protocol (TCP) connections to prevent TCP attacks.

The parameters simple and cipher in the peer { group-name | ipv4-address } password { cipher cipher-password | simple simple-password command only affect password display. The simple parameter indicates that the password is displayed in plain text. The cipher parameter indicates that the password is displayed in cipher text.

2.8.27  Why Are Loopback Addresses Used to Establish BGP Peer Relationships?

Loopback interfaces are logical interfaces. Compared with physical interfaces, loopback interfaces are not affected by links and can reduce the Border Gateway Protocol (BGP) flapping.

2.8.28  Why Is the BGP Connection Not Interrupted Immediately After the Interfaces Connecting Two Peers Are Shut Down?

When External Border Gateway Protocol (EBGP) peers are directly connected and the ebgp-interface-sensitive command is run in the Border Gateway Protocol (BGP) view, the BGP peer relationship is interrupted immediately after the interfaces connecting the two peers are shut down. By default, the ebgp-interface-sensitive command is run in the BGP view. In other cases, the BGP peer relationship is not interrupted until the Hold timer times out.

2.8.29  Why Are All the Next Hop Addresses in the BGP Routing Table Displayed as 0.0.0.0 After BGP Imports Routes from Other Protocols?

Only routes that exist in the Border Gateway Protocol (BGP) routing table can be imported by the BGP. When importing such routes, BGP does not add new routes, but increases the reference count based on the routing table.

2.8.30  Why Can BGP Not Immediately Attempt to Establish Connections After the Peer Is Configured?

To prevent the Border Gateway Protocol (BGP) from frequently tearing down the neighbor relationship for renegotiation, the device waits for a proper period before establishing connections to ensure that related configurations are complete. The recommended period in RFC4271 is 120 seconds. The implementation in AR series routers is 32 seconds.

2.8.31  What Is the Logical Relationship Between the Route-Policy Nodes?

Route-Policy filters routing information and sets route attributes for the routes that match the Route-Policy. The filtering relationship between the Route-Policy nodes is OR. That is, if a route matches a node, the route matches the Route-Policy. If a route does not match any node, the route fails to match the Route-Policy. If the relationship between matching rules is AND, the result is applied only after Route-Policy sends the pass response.

2.8.32  How Do I Set the Delay for Re-applying a Routing Policy

The AR100&AR120&AR150&AR160&AR200&AR1200&AR2200&AR3200&AR3600 provides the following rules for processing changes of a routing policy:

After the command used to configure the routing policy changes, the RM module immediately notifies protocols of the change by default. You can run the route-policy-change notify-delay delay-time command to set the delay when the AR100&AR120&AR150&AR160&AR200&AR1200&AR2200&AR3200&AR3600 notifies protocols of re-applying a routing policy after the routing policy changes. The routing policy is re-applied after the delay.

  • If the configuration of the routing policy changes again during the delay, the RM module resets the timer.

  • If the routing policy is referenced by BGP, you can also run the refresh bgp all command to trigger BGP to apply the routing policy immediately during the delay.

2.8.33  How Does the Device Forward Packets Using Policy-based Routing?

In earlier versions of V200R002C00, policy-based routing takes effect only for traffic delivered by the local device. To select routes for forwarding traffic, configure the redirect function. In V200R002C01 and later versions, policy-based routing (PBR) is categorized into local PBR, interface PBR, and smart policy routing (SPR). Local PBR takes effect only for traffic delivered by the local device and interface PBR takes effect only for traffic forwarded by the device.

Policy-based routing (PBR) is categorized into local PBR, interface PBR, and smart policy routing (SPR). Local PBR takes effect only for traffic delivered by the local device, interface PBR, and smart policy routing take effect only for traffic forwarded by the device.

2.8.34  Failed to Query OSPF Information Through OSPF MIB Objects

The MIB is a virtual database of the device status maintained by managed devices. After creating an OSPF process, you can configure an OSPF MIB object to process the OSPF process, that is, bind the MIB to this OSPF process. If no MIB object is bound to this OSPF process, OSPF information cannot be queried through this OSPF MIB object.

By default, OSPF processes are not bound to SNMP.

A specified OSPF process can be processed through an OSPF MIB object only after this process is bound to SNMP using the ospf mib-binding process-id command.

Similarly:

  • Before using an OSPFv3 MIB object to manage an OSPFv3 process, run the ospfv3 mib-binding process-id command to bind this OSPFv3 process to SNMP.
  • Before using a RIP MIB object to manage a RIP process, run the rip mib-binding process-id command to bind this RIP process to SNMP.

2.8.35  Failed to Establish an OSPF Neighbor Relationship with a BDCOM Router

When a Huawei router communicates with a BDCOM router through OSPF, and the interface network type of the BDCOM router is set to ip ospf network point-to-multipoint non-broadcast, the two routers cannot establish an OSPF neighbor relationship.

The reason is as follows: The interface network type of the BDCOM route has been set to ip ospf network point-to-multipoint non-broadcast, which is similar to P2MP NBMA type; the BDCOM router uses a proprietary protocol but not standard OSPF protocol and so cannot communicate with the Huawei router. To ensure that the two routers establish an OSPF neighbor relationship, change the network types of interfaces on both ends to be consistent and ensure that the two routers communicate using the interface network type specified by the standard OSPF protocol. Huawei routers support four interface network types: broadcast, NBMA, P2P, and P2MP.

From group: Router
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WoodWood
Created Aug 30, 2017 06:21:24

AR Router Maintenance Guide-FAQ(IP Routing)-2430809-1
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wissal
MVE Created Apr 12, 2018 15:04:57

clear and useful document, thanks
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