Setting Up Connections Between the 5620 SAM and the 7705 SAR

IP over ATM is used for in-band management of the 7705 SAR. This requires the use of IP addresses so that the packets can be routed through the network using a routing table to indicate the next hop. Because Apipe interfaces (SAPs) do not have IP addresses, Apipes cannot be used to carry the management traffic.

With IES, the ATM SAP can be used for the forwarding of management IP packets. To set up a connection, IES is enabled on an interface on the 7705 SAR and the IP address for the interface is defined. A PVCC connection is then set up between the 7705 SAR and the remote router (SR) attached to the network manager (5620 SAM).

The IP datagrams are encapsulated into AAL5 for transport over the ATM network.

At the remote SR end, the SAP is bound to a VPRN instance to ensure that LDP signaling to the system IP address of the 7705 SAR flows through the IP/GRE link and not over the ATM link. Within the VPRN, an IP address is assigned at the termination SAP. The IP datagram is extracted from the ATM cell at this termination point and is routed to the 5620 SAM.

Alternatively, manually configured connections can be used instead of signaled pseudowires.

Note: The remote IP address must be manually configured and a static route must be set up between the two connections. This configuration is beyond the scope of this document; refer to the 7705 SAR OS Router Configuration Guide for information.

For redundancy, it is recommended that two VCs be configured per ATM port or IMA group. This requires the configuration of two static routes. ECMP must be enabled to allow duplicate routes in the routing table, and BFD can be enabled to trigger a faster handoff to the other route in case of route failure.

Encapsulation

To run IP traffic over ATM links, the system uses routed VC-mux encapsulation as specified in RFC 2684, Multiprotocol Encapsulation over ATM Adaptation Layer 5. Since the only supported Layer 3 protocol over the management VC is IP, the VC mux encapsulation method is implemented to reduce complexity and overhead; likewise, routing mode is preferred over bridged mode.

The maximum MTU size supported is 2048 bytes.

Layer 2 and Layer 3 Traffic Management

ATM traffic descriptors can be applied at the ingress (policing) and egress (shaping and service category scheduling and prioritization) of the IES SAP in order to provide traffic management functions at Layer 2.

Management IP traffic that is destined for the CSM is classified at Layer 3 and is forwarded into the fabric from one of three of the adapter card control queues:

The high-priority and low-priority queues are limited to 1 Mb/s and the FTP queue is rate-limited to 3 Mb/s ingress to the fabric toward the control plane.

Note: Proper configuration of the traffic descriptor profiles is essential for proper operation of the IES SAP. If no profile is assigned, the default UBR service category is assumed. All IES 7705 SAR traffic is scheduled; no shaping is supported in this mode. To ensure that IP traffic transported over the IES SAP is prioritized fairly, ATM layer traffic descriptors should be assigned. See IES Management SAP Commands in the IES Command Reference section for information.

Troubleshooting and Fault Detection Services

The IES in-band management service supports ATM OAM F4 (VP level) and F5 (VC level) cell generation and termination. For more information on OAM, refer to the 7705 SAR OS OAM and Diagnostics Guide, “OAM and SAA”.

Bidirectional forwarding detection (BFD) can also be configured on the IES interface. BFD is a simple protocol for detecting failures in a network. BFD uses a “hello” mechanism that sends control messages periodically to the far end and receives periodic control messages from the far end. BFD is implemented for static routes in asynchronous mode only, meaning that neither end responds to control messages; rather, the messages are sent in the time period configured at each end.

To support redundancy, ECMP must be enabled to allow duplicate routes in the routing table, and BFD must be enabled to trigger the handoff to the other route in case of failure.

Due to the lightweight nature of BFD, it can detect failures faster than other detection protocols, making it ideal for use in applications such as mobile transport.

If the configured number of consecutive missed BFD messages is reached, the static route to the peer is declared not active.

Note: Layer 2 AIS/RDI cells that are received on the IES SAP will disable the IP interface. Link failures detected by BFD will also disable the IP interface.

IP ECMP Load Balancing

IP ECMP allows the configuration of load balancing across all IP interfaces at the system level or interface level on the network side. You can include Layer 4 port attributes and/or the TEID attribute in the hashing algorithm with the l4-load-balancing and teid-load-balancing commands in the config>service>ies>interface context. Configuration at the interface level overrides the system-level settings for the specific interface.

For more information on IP ECMP, refer to the7705 SAR OS Router Configuration Guide, “Static Routes, Dynamic Routes, and ECMP”.

DHCP Relay and DHCPv6 Relay

The 7705 SAR provides DHCP/BOOTP Relay agent services and DHCPv6 Relay agent services for DHCP clients. DHCP is used for IPv4 network addresses and DHCPv6 is used for IPv6 network addresses. Both DHCP and DHCPv6 are known as stateful protocols because they use dedicated servers to maintain parameter information.

Unless stated otherwise, DHCP is equivalent to “DHCP for IPv4”, or DHCPv4.

In the stateful autoconfiguration model, hosts obtain interface addresses and/or configuration information and parameters from a server. The server maintains a database that keeps track of which addresses have been assigned to which hosts.

The 7705 SAR supports DHCP Relay on access IP interfaces associated with IES and VPRN and on network interfaces. Each DHCP instance supports up to eight DHCP servers.

The 7705 SAR supports DHCPv6 Relay on access IP interfaces associated with IES. Each DHCPv6 instance supports up to eight DHCPv6 servers.

Note: The 7705 SAR acts as a Relay agent for DHCP and DHCPv6 requests and responses; it does not function as a DHCP or DHCPv6 server. When used as a CPE, the 7705 SAR can act as a DHCP client to learn the IP address of the network interface. Dynamic IP address allocation is supported on network interfaces only. Refer to the 7705 SAR OS Router Configuration Guide, “DHCP”, for more information.

IPCP

Similar to DHCP over Ethernet interfaces, Internet Protocol Control Protocol (IPCP) extensions to push IP information over PPP/MLPPP IES SAPs are supported. Within this protocol, extensions can be configured to define the remote IP address and DNS IP address to be signaled via IPCP on the associated PPP interface. The IPCP-based IP and DNS assignment process is similar to DHCP behavior; IPCP-based IP/DNS assignment uses PPP/MLPPP IP layer protocol handshake procedures. PPP/MLPPP connected devices hooked up to IES can benefit from this feature for the assignment of IP and DNS to the associated interface.

IPSec Support

The 7705 SAR supports IPSec and IPSec tunnels, where IES is used as a public (untrusted) network-facing service and VPRN is used as a private (trusted) network-facing service. IES interfaces support the provisioning of tunnel SAPs as part of IPSec provisioning. The sap-id for a tunnel SAP is tunnel-1.public:tag.

For more information, see the IPSec chapter in this guide.

NAT and IES

Network Address Translation (NAT) is used by mobile backhaul, enterprise, and SI (Strategic Industries) providers to provide expandability and security for private networks. Tier 1 providers can potentially run out of private IPv4 addresses, making it difficult to expand their existing networks. To address this issue, NAT can be used. NAT can hide multiple private IP addresses behind a single public IP address and therefore makes it possible to scale IP solutions in mobile backhaul, enterprise, and SI networks.

Besides conserving available IPv4 addresses, NAT can also be used as a security feature to hide the real IP addresses of hosts, securely providing private LAN users access to public addresses.

NAT configuration is based on zones. Zones segment a network, making it easier to control and organize traffic. A zone consists of a group of Layer 3 interfaces with common criteria, bundled together. NAT policies, which define a set of rules that determine how NAT should direct traffic, can be applied to the entire zone.

A zone can be configured within the router context or under the base router and/or within the IES or VPRN service context. A zone is configured by adding at least one Layer 3 interface to the zone configuration. Multiple zones can be created within each service or within the router context. Layer 3 interfaces from different services cannot be grouped into a single common zone.

Note: NAT on IES does not support spoke SDP termination.

Proxy ARP

Proxy ARP is supported on IES interfaces.

Proxy ARP is a technique by which a router on one network responds to ARP requests intended for another node that is physically located on another network. The router effectively pretends to be the destination node by sending an ARP response to the originating node that associates the router’s MAC address with the destination node’s IP address (acts as a proxy for the destination node). The router then takes responsibility for routing traffic to the real destination.

For more information on proxy ARP, refer to the 7705 SAR OS Router Configuration Guide, “Proxy ARP”.

Configurable ARP Retry Timer

A timer is available to configure a shorter retry interval when an ARP request fails. An ARP request may fail for a number of reasons, such as network connectivity issues. By default, the 7705 SAR waits 5000 ms before retrying an ARP request. The configurable retry timer makes it possible to shorten the retry interval to between 100 and 30 000 ms.

Note: The ARP retry default value of 5000 ms is intended to protect CPU cycles on the 7705 SAR, especially when it has a large number of interfaces. Configuring the ARP retry timer to a value shorter than the default should be done only on mission-critical links, such as uplinks or aggregate spoke SDPs transporting mobile traffic; otherwise, the retry interval should be left at the default value.

The configurable ARP retry timer is supported on VPRN and IES service interfaces, as well on the router interface.

Troubleshooting and Fault Detection Services

Bidirectional forwarding detection (BFD) can be configured on the IES interface. BFD is a simple protocol for detecting failures in a network. BFD uses a “hello” mechanism that sends control messages periodically to the far end and expects to receive periodic control messages from the far end. On the 7705 SAR, BFD is implemented for static routes in asynchronous mode only, meaning that neither end responds to control messages; rather, the messages are sent periodically from each end.

To support redundancy with fast switchover, BFD must be enabled to trigger the handoff to the other route in case of failure.

Due to the lightweight nature of BFD, it can detect failures faster than other detection protocols, making it ideal for use in applications such as mobile transport.

If BFD packets are not received in the configured amount of time, the associated static route is declared “not active”, causing a reroute to an alternative path, if any.

Note: Link failures detected by BFD will disable the IP interface.

The 7705 SAR also supports Internet Control Message Protocol (ICMP and ICMPv6). ICMP is a message control and error reporting protocol that also provides information relevant to IP packet processing. For more information on ICMP and ICMPv6, refer to the 7705 SAR OS Router Configuration Guide, “ICMP and ICMPv6”.

SAPs

This section contains information on the following topics:

Spoke SDP Termination to IES

This feature enables a customer to exchange traffic between a VLL or VPLS (Layer 2) service and an IES or VPRN (Layer 3) service. Customer premises traffic coming in from a VLL or VPLS service (SAP to spoke SDP) is forwarded over the IP/MPLS network to the IES or VPRN service, and vice versa. Network QoS policies can be applied to the spoke SDP to control traffic forwarding to the Layer 3 service.

In a Layer 3 spoke SDP termination to an IES or VPRN service, where the destination IP address resides within the IES or VPRN network, CE device-generated ARP frames must be processed by the Layer 3 interface. When an ARP frame is received over the spoke SDP at the Layer 3 interface endpoint, the 7705 SAR responds to the ARP frame with its own MAC address. When an ARP request is received from the routed network and the ARP entry for the CE device that is connected to the spoke SDP is not known, the 7705 SAR initiates an ARP frame to resolve the MAC address of the next hop or CE device.

Figure 84 shows traffic terminating on a specific IES or VPRN service that is identified by the SDP ID and VC label present in the service packet.

Figure 84:  SDP ID and VC Label Service Identifiers (Conceptual View of the Service) 

Figure 85 shows a spoke SDP terminating directly into an IES. In this case, a spoke SDP could be tied to an Epipe or a hierarchical VPLS service. There is no configuration required on the PE connected to the CE.

Figure 85:  IES Spoke SDP Termination 

Ethernet spoke SDP termination for IES is supported over the following network uplinks:

Spoke SDP termination for IES supports the following:

A spoke SDP on an IES interface can be connected to the following entities:

Figure 86 shows an example of backhauling from a given site that uses PW and IES on the 7705 SAR. An individual PW is configured on a per-CE device or a per-service basis. For routing services, this PW can be terminated to an IES at the 7750 SR end. This scenario offers per-service OAM and redundancy capabilities. Because there is no local communication on the remote 7705 SAR, traffic between any two devices connected to the 7705 SAR must traverse through the 7750 SR at the MTSO/CO.

Figure 86:  Pseudowire-Based Backhaul (Spoke SDP Termination at 7750 SR)