AS13380 ASN-CUST - Zix Corporation

The same reverse name is attached to addresses in two different blocks, and one of them is a customer's own brand.

What it's used for

• The network of a secure email and messaging provider. 6,912 addresses across five IPv4 prefixes, four observed BGP neighbours, and the IPv6 block 2620:12d:6000::/47.

Notable

• Netnames span four company identities: VZ-63-71-8-0 and ZIXCORP, CM2-A-BLK-1 registered to a content management corporation, and LVLT-APPRI-1-8-19-116 on two blocks registered to a third company.
• Sampled names include the literal words network.zixcorp.com and broadcast.zixcorp.com.
• network.zixcorp.com answers for addresses in two different prefixes.
• Another name reads securemail- followed by a law firm's own domain.

Interesting

• One reverse name serving two addresses in unrelated blocks is allowed by the protocol and breaks the assumption almost every tool makes, which is that a reverse lookup identifies a single host. Here it identifies a role that exists once per block.
• Naming network and broadcast addresses with those exact words is a habit from hand-built zones, preserved into a network large enough that everything else is generated.
• The customer's domain appearing inside the provider's address space is how hosted secure email works: the recipient sees the sender's brand, and the address underneath belongs to the platform.
• Two carrier-formatted netnames mean two of these blocks were never held directly but assigned by upstreams, and the acquisitions since have left four names in one routing table entry set.