Expressway business-to-business calling

See also

Sources

1. 1
   Cisco's Preferred Architecture recommends Expressway-E automated detection, which blocks an offending source IP in the internal firewall for a configurable period after a configurable number of rejections.

   Preferred Architecture for Cisco Collaboration 14 Enterprise On-Premises Deployments, CVD - Security · Toll Fraud Mitigation > Cisco Expressway · Checked 2026-09-25
2. 2
   Cisco advises avoiding the Any wildcard for a search rule's Source to minimise toll-fraud risk.

   Cisco Expressway Administrator Guide (X15.4) - Dial Plan and Call Processing · Search rule examples (emergency/911 rule example note) · Checked 2026-09-25
3. 3
   Expressway Call Policy mode can be Off, Local CPL (web-configured rules or an uploaded CPL script, mutually exclusive) or Policy service (an external service decides).

   Cisco Expressway Administrator Guide (X15.4) - Dial Plan and Call Processing · Configuring Call Policy: Call policy mode · Checked 2026-09-25
4. 4
   With a cluster of Expressway-Es, DNS A and SRV records must be set up for each peer in the cluster.

   Cisco Expressway-E and Expressway-C Basic Configuration Deployment Guide (X14.0) - DNS Records · DNS Records: note on Expressway-E clusters · Checked 2026-09-25
5. 5
   Cisco's example toll-fraud CPL rejects gateway-zone calls that would hairpin back out of the ISDN gateway with status 403, and can optionally reject unauthenticated callers dialling the gateway prefix 9.

   Cisco Expressway-E and Expressway-C Basic Configuration Deployment Guide (X14.0) - Optional Configuration Tasks · Task 22: example CPL · Checked 2026-09-25
6. 6
   Toll-fraud CPL is applied by setting Configuration > Call Policy > Configuration to Call policy mode Local CPL and uploading the CPL file, which the Expressway checks and rejects with an XML invalid error if malformed.

   Cisco Expressway-E and Expressway-C Basic Configuration Deployment Guide (X14.0) - Optional Configuration Tasks · Task 22: Restricting access to ISDN gateways (toll-fraud prevention) · Checked 2026-09-25
7. 7
   For SIP/TLS between Unified CM and Expressway-C, the Expressway-C server certificate or its CA root goes into the Unified CM trust store on all servers, and the CallManager certificate or its CA root goes into Expressway-C's trusted CA list.

   Configure Business to Business Audio/Video Calls through Expressway · Configure: certificates · Checked 2026-09-25
8. 8
   Cisco's B2B technote has the Unified CM SIP trunk to Expressway-C listen on non-standard ports 6060 for SIP/TCP and 6061 for SIP/TLS, keeping B2B traffic apart from MRA edge traffic.

   Configure Business to Business Audio/Video Calls through Expressway · Configure: neighbor zone to Unified CM and Unified CM SIP trunk · Checked 2026-09-25
9. 9
   Cisco's Collaboration 14 Preferred Architecture recommends CPL rules to allow or reject calls from the Default Zone in B2B deployments, for example rejecting inbound B2B calls to 9-prefixed destinations to block unauthorised PSTN calls.

   Preferred Architecture for Cisco Collaboration 14 Enterprise On-Premises Deployments, CVD - Security · Toll Fraud Mitigation > Cisco Expressway · Checked 2026-09-25
10. 10
    If the target domain publishes no NAPTR records, the Expressway uses a default list of _sips._tcp, _sip._tcp and _sip._udp SRV queries for that domain.

    Cisco Expressway Administrator Guide (X15.2) - Dial Plan and Call Processing · URI Resolution Process Using DNS (SIP) · Checked 2026-09-25
11. 11
    Default Zone access rules (Configuration > Zones > Default Zone access rules) control which external systems may connect to the Expressway over SIP TLS via the Default Zone.

    Cisco Expressway Administrator Guide (X15.4) - Zones and Neighbors · Default Zone access rules · Checked 2026-09-25
12. 12
    The Default Zone represents incoming calls from endpoints or devices that are unregistered or not recognised, which is where unsolicited inbound B2B calls arrive.

    Cisco Expressway Administrator Guide (X15.4) - Zones and Neighbors · The Default Zone · Checked 2026-09-25
13. 13
    All calls through the Default Zone consume Rich Media Session (RMS) licences, so appropriate zones and rules should be created to avoid needless RMS consumption.

    Cisco Expressway Administrator Guide (X15.4) - Zones and Neighbors · The Default Zone: RMS licence note · Checked 2026-09-25
14. 14
    Cisco's example DNS-zone search rule uses a negative-lookahead regex so calls to the organisation's own domain are never looked up on public DNS, while calls to other domains are.

    Cisco Expressway-E and Expressway-C Basic Configuration Deployment Guide (X14.0) - Routing Configuration · Routing Configuration: DNS zone search rule (priority 150, pattern excluding @example.com) · Checked 2026-09-25
15. 15
    Cisco's example DNS zone uses H.323 mode On, SIP mode On, fallback transport TCP and Include address record Off.

    Cisco Expressway-E and Expressway-C Basic Configuration Deployment Guide (X14.0) - Routing Configuration · Routing Configuration: DNS zone settings table · Checked 2026-09-25
16. 16
    A DNS zone is used to search for externally hosted systems, as in business-to-business calling, and a DNS search rule defines when that zone is searched.

    Cisco Expressway-E and Expressway-C Basic Configuration Deployment Guide (X14.0) - Routing Configuration · Routing Configuration: DNS zone · Checked 2026-09-25
17. 17
    A DNS zone's TLS verify setting controls whether the Expressway checks the X.509 certificate of the destination server returned by the DNS lookup.

    Cisco Expressway Administrator Guide (X15.4) - Zones and Neighbors · Configuring DNS Zones: TLS verify mode · Checked 2026-09-25
18. 18
    In Cisco's basic configuration example the local-zone rule is priority 50, the traversal-zone rule priority 100 and the DNS-zone rule priority 150, each set to Continue on successful match.

    Cisco Expressway-E and Expressway-C Basic Configuration Deployment Guide (X14.0) - Routing Configuration · Routing Configuration: search rules tables · Checked 2026-09-25
19. 19
    A DNS zone's Fallback transport sets the SIP transport used when NAPTR records and SIP URI parameters give no preferred transport.

    Cisco Expressway Administrator Guide (X15.4) - Zones and Neighbors · Configuring DNS Zones: Fallback transport protocol · Checked 2026-09-25
20. 20
    Field reports describe internet bots sending SIP INVITE and OPTIONS to Expressway-E at around 2 to 3 per second, trying varied called patterns to find a PSTN route and spoofing the organisation's own domain or the Expressway IP as caller.field report

    Securing Expressway Deployment from Spam & Toll Fraud Calls · Observed attack patterns section · Checked 2026-09-25
21. 21
    Cisco recommends turning off any H.323 and SIP protocol support (ALG) on the firewall in front of the Expressway.

    Cisco Expressway Administrator Guide (X15.4) - Firewall Traversal · Firewall configuration · Checked 2026-09-25
22. 22
    The Expressway uses _h323ls._udp SRV records for H.323 location services and _h323cs._tcp SRV records for H.323 call signalling.

    Cisco Expressway Administrator Guide (X15.4) - Dial Plan and Call Processing · Configuring H.323 SRV Records · Checked 2026-09-25
23. 23
    For H.323 firewall traversal a traversal zone can use either Assent or H.460.18, while SIP traversal uses Assent over a TCP/TLS connection from client to server.

    Cisco Expressway Administrator Guide (X15.4) - Firewall Traversal · Firewall traversal protocols (Assent, H.460.18/19) · Checked 2026-09-25
24. 24
    Expressway hop count ranges from 1 to 255 with a default of 15, decreasing by one each time a request is forwarded; for URI or ENUM dialling the hop count of the DNS or ENUM zone is used.

    Cisco Expressway Administrator Guide (X15.4) - Dial Plan and Call Processing · Hop counts · Checked 2026-09-25
25. 25
    For external systems to reach a domain by URI dialing, the domain must publish the appropriate DNS SRV and A/AAAA records.

    Cisco Expressway Administrator Guide (X15.4) - Dial Plan and Call Processing · URI Dialing via DNS for Incoming Calls · Checked 2026-09-25
26. 26
    When Include address record is enabled on a DNS zone, the Expressway queries for A or AAAA records, and if any are found it does not query lower-priority zones.

    Cisco Expressway Administrator Guide (X15.4) - Zones and Neighbors · Configuring DNS Zones: Include address record · Checked 2026-09-25
27. 27
    With the default Registered only mode, a B2B call between a Unified CM SIP user and an external H.323-only system through Expressways with no locally registered endpoint would probably not be interworked unless the mode is changed to On.inferred

    Cisco Expressway Administrator Guide (X15.4) - Protocols · Configuring H.323 and SIP Interworking · Checked 2026-09-25
28. 28
    The default H.323-SIP interworking mode is Registered only, and Cisco recommends leaving it at that setting.

    Cisco Expressway Administrator Guide (X15.4) - Protocols · Configuring H.323 and SIP Interworking: H.323 <-> SIP interworking mode · Checked 2026-09-25
29. 29
    The Expressway's H.323-SIP interworking mode can be Off, Registered only (interwork only if at least one endpoint is locally registered) or On (interwork regardless of registration).

    Cisco Expressway Administrator Guide (X15.4) - Protocols · Configuring H.323 and SIP Interworking · Checked 2026-09-25
30. 30
    If Local CPL is enabled but no policy is configured or uploaded, a default policy is applied that allows all calls.

    Cisco Expressway Administrator Guide (X15.4) - Dial Plan and Call Processing · Configuring Call Policy · Checked 2026-09-25
31. 31
    The DNS zone's Modify DNS request option routes outbound SIP calls to a manually specified SIP domain instead of the domain in the dialled destination.

    Cisco Expressway Administrator Guide (X15.4) - Zones and Neighbors · Configuring DNS Zones: Modify DNS request · Checked 2026-09-25
32. 32
    Expressway-E and Expressway-C must not share an address behind NAT, because the firewall cannot distinguish between them.

    Cisco Expressway Administrator Guide (X15.4) - Firewall Traversal · Firewall traversal: network address guidance · Checked 2026-09-25
33. 33
    Cisco's example public DNS for H.323 publishes _h323cs._tcp on port 1720 for call signalling, plus _h323ls._udp and _h323rs._udp on port 1719, all targeting the Expressway-E.

    Cisco Expressway-E and Expressway-C Basic Configuration Deployment Guide (X14.0) - DNS Records · DNS Records: public DNS records table (Expressway-E) · Checked 2026-09-25
34. 34
    Cisco's example public DNS for the Expressway-E publishes _sips._tcp on port 5061, _sip._tcp on port 5060 and _sip._udp on port 5060, each targeting the Expressway-E host A record.

    Cisco Expressway-E and Expressway-C Basic Configuration Deployment Guide (X14.0) - DNS Records · DNS Records: public DNS records table (Expressway-E) · Checked 2026-09-25
35. 35
    For inbound SIP business-to-business calls, SRV records for SIP call routing must be created on the public DNS servers so other organisations can locate the Expressway-E.

    Configure Business to Business Audio/Video Calls through Expressway · Configure section: DNS SRV records for SIP call routing · Checked 2026-09-25
36. 36
    Cisco's Expressway release-note listing shows an X15.5.x release note alongside X15.4.x (dated 13 April 2026) and X15.3.x (dated 6 January 2026).

    Cisco Expressway Series - Release Notes · X15.x release notes list entries · Checked 2026-09-25
37. 37
    A search rule's Request must be authenticated option restricts the rule to requests from authenticated devices.

    Cisco Expressway Administrator Guide (X15.4) - Dial Plan and Call Processing · Configuring Search Rules: Request must be authenticated · Checked 2026-09-25
38. 38
    RFC 3263 specifies that when no SRV records exist, the client does an A or AAAA lookup of the domain and uses the transport's default port (5060, or 5061 for TLS).

    RFC 3263: Session Initiation Protocol (SIP): Locating SIP Servers · Section 4.2 Determining Port and IP Address · Checked 2026-09-25
39. 39
    RFC 3263 specifies that if no NAPTR records are found, a SIP client constructs SRV queries for the transports it supports.

    RFC 3263: Session Initiation Protocol (SIP): Locating SIP Servers · Section 4.1 Selecting a Transport Protocol · Checked 2026-09-25
40. 40
    The Expressway processes a call by applying pre-search transforms, then Call Policy, then User Policy (FindMe), then search rules, and restarts the process whenever a new alias results.

    Cisco Expressway Administrator Guide (X15.4) - Dial Plan and Call Processing · Call Routing Process · Checked 2026-09-25
41. 41
    Search rule priorities range from 1 to 2000, with lower numbers taking higher priority, and every applicable target is queried when several rules match at the same priority.

    Cisco Expressway Administrator Guide (X15.4) - Dial Plan and Call Processing · Configuring Search Rules: Priority · Checked 2026-09-25
42. 42
    A search rule's Source can be Any (including unregistered devices and the public internet), All zones (local zone and configured zones only), Local Zone (registered devices only) or Named.

    Cisco Expressway Administrator Guide (X15.4) - Dial Plan and Call Processing · Configuring Search Rules: Source · Checked 2026-09-25
43. 43
    On successful match, Stop halts processing of lower-priority search rules, but other rules at the same priority are still applied.

    Cisco Expressway Administrator Guide (X15.4) - Dial Plan and Call Processing · Configuring Search Rules: On successful match · Checked 2026-09-25
44. 44
    Cisco's B2B technote uses a traversal zone separate from the Unified Communications (MRA) traversal zone, on a different port such as 7003 rather than 7001.

    Configure Business to Business Audio/Video Calls through Expressway · Configure: traversal zone for B2B · Checked 2026-09-25
45. 45
    Cisco's Preferred Architecture also cites a SIP rate-limiting capability, configured with a maximum connections per second and a maximum burst size, as a toll-fraud mitigation.

    Preferred Architecture for Cisco Collaboration 14 Enterprise On-Premises Deployments, CVD - Security · Toll Fraud Mitigation > Cisco Expressway · Checked 2026-09-25
46. 46
    In the X15.4 SIP protocol configuration the default transport modes are UDP Off, TCP Off, TLS On and Mutual TLS Off.

    Cisco Expressway Administrator Guide (X15.4) - Protocols · Protocols > SIP > Configuring SIP (transport mode defaults) · Checked 2026-09-25
47. 47
    SIP over UDP is disabled by default on the Expressway, so a published _sip._udp record does not work unless UDP is enabled.

    Cisco Expressway-E and Expressway-C Basic Configuration Deployment Guide (X14.0) - DNS Records · DNS Records: public DNS records table, _sip._udp row note · Checked 2026-09-25
48. 48
    Cisco's B2B audio/video technote states minimum versions of Expressway X8.1.1 and Unified CM 10.0.

    Configure Business to Business Audio/Video Calls through Expressway · Requirements / Components Used · Checked 2026-09-25
49. 49
    The Expressway supports up to 100 pre-search transforms with unique priorities from 1 to 65534, and only one transform can match per search.

    Cisco Expressway Administrator Guide (X15.4) - Dial Plan and Call Processing · About Pre-Search Transforms · Checked 2026-09-25
50. 50
    Pre-search transforms normalise aliases from H.323 and SIP devices before zones are searched, for example by appending the organisation's domain to an E.164 alias to form a SIP URI.

    Cisco Expressway-E and Expressway-C Basic Configuration Deployment Guide (X14.0) - Routing Configuration · Routing Configuration: Pre-search Transforms · Checked 2026-09-25
51. 51
    The B2B technote uses a transform on Expressway-C to remove the port from the URI in INVITEs received from Unified CM.

    Configure Business to Business Audio/Video Calls through Expressway · Configure: Dialplan with transforms and search rules · Checked 2026-09-25
52. 52
    Traversal clients must always authenticate to the traversal server, and each traversal client zone specifies a username and password.

    Cisco Expressway Administrator Guide (X15.4) - Zones and Neighbors · Configuring traversal client zones: authentication · Checked 2026-09-25
53. 53
    Expressway supports traversal chaining, in which the first Expressway-E is the traversal server to Expressway-C and a traversal client to a second Expressway-E.

    Cisco Expressway Administrator Guide (X15.4) - Firewall Traversal · Firewall traversal chaining · Checked 2026-09-25
54. 54
    Both the traversal client and the traversal server must be Cisco Expressway systems; neither can be a Cisco VCS.

    Cisco Expressway Administrator Guide (X15.4) - Firewall Traversal · Firewall traversal: requirements · Checked 2026-09-25
55. 55
    A traversal client keeps a connection open through the firewall to a designated port on the traversal server using keepalives, and the server sends incoming call requests to the client over that connection.

    Cisco Expressway Administrator Guide (X15.4) - Firewall Traversal · How firewall traversal works · Checked 2026-09-25
56. 56
    The default traversal media port range is 36000 to 59999.

    Cisco Expressway Administrator Guide (X15.4) - Firewall Traversal · Media port ranges / Traversal Subzone · Checked 2026-09-25
57. 57
    Cisco guidance numbers traversal zone ports from TCP 7001 for SIP and UDP 6001 for H.323, incrementing by one for each additional traversal zone.

    Cisco Expressway Administrator Guide (X15.4) - Firewall Traversal · Ports for initial connections from traversal clients · Checked 2026-09-25
58. 58
    In a B2B deployment Expressway-C is the traversal client and Expressway-E is the traversal server.

    Configure Business to Business Audio/Video Calls through Expressway · Configure: traversal zone on Expressway-C and Expressway-E · Checked 2026-09-25
59. 59
    For URI dialing, the Expressway queries NAPTR records first, then SRV records, then A or AAAA records.

    Cisco Expressway Administrator Guide (X15.4) - Dial Plan and Call Processing · URI Resolution Process Using DNS · Checked 2026-09-25
60. 60
    Expressway zone types are Neighbor, Traversal client, Traversal server, DNS, ENUM and Unified Communications traversal, plus a built-in Default Zone.

    Cisco Expressway Administrator Guide (X15.4) - Zones and Neighbors · Zones and Neighbors: About zones / zone types · Checked 2026-09-25

Documents

Cite this page

WarmTransfer. (2026, September 25). Expressway business-to-business calling. WarmTransfer. https://warmtransfer.net/knowledge/expressway-b2b-calling

@misc{warmtransfer-expressway-b2b-calling,
  title  = {Expressway business-to-business calling},
  author = {{WarmTransfer}},
  year   = {2026},
  url    = {https://warmtransfer.net/knowledge/expressway-b2b-calling},
  note   = {Verified 2026-09-25}
}