Cisco Systems ASR 1000 Local Source Properties Address and Port, Locally Hairpinned Sessions

Chapter 7 H.248 Services—Signaling and Control

Local Source Properties (Address and Port)

DBE Restrictions

The following are restrictions of DBE support for the Flexible Address Prefix Provisioning feature:

•Only three different lengths of network masks can be in use on a given shared address at one time.

•When multiple mask lengths are used on a shared local address, there is extra overhead of hash key construction and flow entry lookup.

Local Source Properties (Address and Port)

The Local Source Properties (Address and Port) feature is described in the “Local Source Properties (Address and Port)” section on page 8-4.

Locally Hairpinned Sessions

The DBE supports hairpinning of calls between subscribers connected to the same DBE for IPv4 and IPv6 packets. A hairpin consists of two pinholes or two pairs of terminations on the DBE that the media gateway controller (MGC) has provisioned with local and remote addresses whereby media from one pinhole should travel directly (loops back) to the other pinhole. The MGC (also known as an SBE) does not differentiate whether Add requests are sent to the same or different DBEs for a flow setup.

In a hairpin media call flow setup, two pairs of terminations internally connect the backbone (BB) side to logically merge two separate DBEs into one DBE. The flow resembles a hairpin.

This feature is useful for interoperation with signaling border elements (SBEs) that provision two pinholes, even in the case where the SBE does not require media to be sent further into the network.

Note Pinhole is an informal term for a pair of terminations in the same stream and same context.

Twice NAPT Pinhole Hairpinning

The DBE successfully forwards media through Twice Network Address and Port Translation (NAPT) pinholes that form a hairpin. For Twice NAPT hairpinning, the DBE forwards media on demand. The SBE sees no differences between Twice NAPT hairpins and Twice NAPT non-hairpins.

When forwarding media, a hairpin behaves the way two separate pinholes behave, except that a packet going through a coupled pair has its IP Time-to-Live counter decremented only once, not twice.

Note Twice NAPT is only supported on IPv4.

No NAPT Pinhole Hairpinning

No NAPT pinholes can form hairpins only under the following circumstances:

•Both pinholes are No NAPT.

Cisco IOS XE Integrated Session Border Controller Configuration Guide for the Cisco ASR 1000 Series Aggregation Services Routers

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