ServerIron ADX Switch and Router Guide

12.0.00

June 10, 2009

Overview

ServerIron ADX supports Internet Protocol (IP) version 4. IP support on Brocade Layer 2 Switches consists of basic services to support management access and access to a default gateway. IP support on ServerIron ADX includes all of the following, in addition to a highly configurable implementation of basic IP services including Address Resolution Protocol (ARP), ICMP Router Discovery Protocol (IRDP), and Reverse ARP (RARP):

•	Route exchange protocols

•	Routing Information Protocol (RIP)

•	Open Shortest Path First (OSPF)

•	Router redundancy protocols

•	Virtual Router Redundancy Protocol Extended (VRRPE)

•	Virtual Router Redundancy Protocol (VRRP)

•	Brocade Standby Router Protocol (FSRP)

IP Interfaces

ServerIron ADX switches allow you to configure IP addresses. With router code installed, IP addresses are associated with individual interfaces. With swtich code installed, a single IP address serves as the management access address for the entire device.

ServerIron ADX switches support configuration and display of IP address in classical subnet format (example: 192.168.1.1 255.255.255.0) and Classless Interdomain Routing (CIDR) format (example: 192.168.1.1/24). You can use either format when configuring IP address information. IP addresses are displayed in classical subnet format by default but you can change the display format to CIDR. See “Changing the Network Mask Display to Prefix Format”.

ServerIron ADX with Router Code Installed

ServerIron ADX switches with router code installed allow you to configure IP addresses on the following types of interfaces:

•	Ethernet ports

•	Virtual routing interfaces (used by VLANs to route among one another)

•	Loopback interfaces

Each IP address on a ServerIron ADX switch with router code must be in a different subnet. You can have only one interface that is in a given subnet. For example, you can configure IP addresses 192.168.1.1/24 and 192.168.2.1/24 on the same ServerIron ADX, but you cannot configure 192.168.1.1/24 and 192.168.1.2/24 on the same ServerIron ADX.

You can configure multiple IP addresses on the same interface.

You can use any of the IP addresses you configure on the ServerIron ADX for Telnet, Web management, or SNMP access.

ServerIron ADX with Switch Code Installed

You can configure an IP address on a ServerIron ADX with switch code for management access to the it. An IP address is required for Telnet access, Web management access, and SNMP access.

You also can specify the default gateway for forwarding traffic to other subnets.

The following sections describe the IP tables and caches:

•	ARP cache and static ARP table

•	IP route table

•	IP forwarding cache

The software enables you to display these tables. You also can change the capacity of the tables on an individual basis if needed by changing the memory allocation for the table.

ARP Cache and Static ARP Table

The ARP cache contains entries that map IP addresses to MAC addresses. Generally, the entries are for devices that are directly attached to the Layer 3 Switch.

An exception is an ARP entry for an interface-based static IP route that goes to a destination that is one or more router hops away. For this type of entry, the MAC address is either the destination device’s MAC address or the MAC address of the router interface that answered an ARP request on behalf of the device, using proxy ARP.

ARP Cache

The ARP cache can contain dynamic (learned) entries and static (user-configured) entries. The software places a dynamic entry in the ARP cache when the Layer 3 Switch learns a device’s MAC address from an ARP request or ARP reply from the device.

The software can learn an entry when the Layer 2 Switch or Layer 3 Switch receives an ARP request from another IP forwarding device or an ARP reply. Here is an example of a dynamic entry:

Each entry contains the destination device’s IP address and MAC address.

Static ARP Table

In addition to the ARP cache, Layer 3 Switches have a static ARP table. Entries in the static ARP table are user-configured. You can add entries to the static ARP table regardless of whether the device the entry is for is connected to the Layer 3 Switch.

NOTE: The Layer 3 Switches have a static ARP table but Layer 2 Switches do not.

The software places an entry from the static ARP table into the ARP cache when the entry’s interface comes up.

Here is an example of a static ARP entry:

Index IP Address MAC Address Port
1 207.95.6.111 0800.093b.d210 1/1

Each entry lists the information you specified when you created the entry.

To display ARP entries, see the following:

•	“Displaying the ARP Cache” – Layer 3 Switch

•	“Displaying the Static ARP Table” – Layer 3 Switch only

•	“Displaying ARP Entries” – Layer 2 Switch

To configure other ARP parameters, see the following:

•	“Configuring ARP Parameters” – Layer 3 Switch only

IP Route Table

The IP route table contains paths to IP destinations.

NOTE: Layer 2 Switches do not have an IP route table. A Layer 2 Switch sends all packets addressed to another subnet to the default gateway, which you specify when you configure the basic IP information on the Layer 2 Switch.

The IP route table can receive the paths from the following sources:

•	A directly-connected destination, which means there are no router hops to the destination

•	A static IP route, which is a user-configured route

•	A route learned through RIP

•	A route learned through OSPF

The IP route table contains the best path to a destination.

•	When the software receives paths from more than one of the sources listed above, the software compares the administrative distance of each path and selects the path with the lowest administrative distance. The administrative distance is a protocol-independent value from 1 – 255.

•	When the software receives two or more best paths from the same source and the paths have the same metric (cost), the software can load share traffic among the paths based on destination host or network address (based on the configuration and the Layer 3 Switch model).

Here is an example of an entry in the IP route table:

Each IP route table entry contains the destination’s IP address and subnet mask and the IP address of the next-hop router interface to the destination. Each entry also indicates the port attached to the destination or the next-hop to the destination, the route’s IP metric (cost), and the type. The type indicates how the IP route table received the route.

To display the IP route table, see the following:

•	“Displaying the IP Route Table” – Layer 3 Switch only

To configure a static IP route, see the following:

•	“Configuring Static Routes” – Layer 3 Switch only

To clear a route from the IP route table, see the following:

•	“Clearing IP Routes” – Layer 3 Switch only

•	For learned routes, modify the ip-route parameter.

•	For static routes, modify the ip-static-route parameter.

IP Forwarding Cache

The IP forwarding cache provides a fast-path mechanism for forwarding IP packets. The cache contains entries for IP destinations. When a Brocade Layer 3 Switch has completed processing and addressing for a packet and is ready to forward the packet, the device checks the IP forwarding cache for an entry to the packet’s destination.

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If the cache contains an entry with the destination IP address, the device uses the information in the entry to forward the packet out the ports listed in the entry. The destination IP address is the address of the packet’s final destination. The port numbers are the ports through which the destination can be reached.

•	If the cache does not contain an entry and the traffic does not qualify for an entry in the session table instead, the software can create an entry in the forwarding cache.

Each entry in the IP forwarding cache has an age timer. If the entry remains unused for ten minutes, the software removes the entry. The age timer is not configurable.

Since routing is supported in hardware, packets hitting routing table entries in TCAM will be routed by hardware without CPU intervention. Only packets destined to direct-connected hosts will show up in the forwarding cache since their first packets will hit the CPU before hardware entries are programmed. Once procrammed in hardware, packets destined to direct-connected hosts will no longer be forwarded to the CPU untill they are aged out.

Here is an example of an entry in the IP forwarding cache:

Each IP forwarding cache entry contains the IP address of the destination, and the IP address and MAC address of the next-hop router interface to the destination. If the destination is actually an interface configured on the Layer 3 Switch itself, as shown here, then next-hop information indicates this. The port through which the destination is reached is also listed, as well as the VLAN and Layer 4 QoS priority associated with the destination if applicable.

To display the IP forwarding cache, see “Displaying the Forwarding Cache”.

NOTE: You cannot add static entries to the IP forwarding cache, although the ServerIron ADX does have options to optimize the cache and increase the number of entries the cache can contain. See “Displaying and Modifying System Parameter Default Settings” for more information.

To increase the size of the IP forwarding cache, see “Displaying and Modifying System Parameter Default Settings” for more information.

IP Route Exchange Protocols

Brocade Layer 3 Switches support the following IP route exchange protocols:

•	Routing Information Protocol (RIP)

•	Open Shortest Path First (OSPF)

•	Border Gateway Protocol version 4 (BGP4)

All these protocols provide routes to the IP route table. You can use one or more of these protocols, in any combination. The protocols are disabled by default. For configuration information, see the following:

•	“Configuring RIP”

•	“Configuring OSPF”

IP Interface Redundancy Protocols

You can configure a Brocade Layer 3 Switch to back up an IP interface configured on another Brocade Layer 3 Switch. If the link for the backed up interface becomes unavailable, the other Layer 3 Switch can continue service for the interface. This feature is especially useful for providing a backup to a network’s default gateway.

Brocade Layer 3 Switches support the following IP interface redundancy protocols:

•	Virtual Router Redundancy Protocol (VRRP) – A standard router redundancy protocol based on RFC 2338. You can use VRRP to configure Brocade Layer 3 Switches and third-party routers to back up IP interfaces on other Brocade Layer 3 Switches or third-party routers.

•	Virtual Router Redundancy Protocol Extended (VRRPE) – A Brocade extension to standard VRRP that adds additional features and overcomes limitations in standard VRRP. You can use VRRPE only on Brocade Layer 3 Switches.

•	Brocade Standby Router Protocol (FSRP) – A Brocade router redundancy protocol developed before VRRP and VRRPE that provides some of the features of VRRP and some of the features of VRRPE. You can use FSRP only on Brocade Layer 3 Switches.

For configuration information, see the following:

•	Virtual Router Redundancy Protocol Extended (VRRPE) – see “Configuring VRRP and VRRP-E”.

•	Virtual Router Redundancy Protocol (VRRP) – see “Configuring VRRP and VRRP-E”.

Access Control Lists and IP Access Policies

Brocade Layer 3 Switches provide two mechanisms for filtering IP traffic:

•	Access Control Lists (ACLs)

•	IP access policies

Both methods allow you to filter packets based on Layer 3 and Layer 4 source and destination information.

ACLs also provide great flexibility by providing the input to various other filtering mechanisms such as route maps, which are used by BGP4. ACLs also provide the input for Policy-Based Routing (PBR), which allows you to selectively modify and route IP packets based on their source IP address.

IP access policies allow you to configure QoS based on sessions (Layer 4 traffic flows).

Only one of these filtering mechanisms can be enabled on a Brocade device at a time. Brocade devices can store forwarding information for both methods of filtering in the session table.