# Network Tools

Published articles for Network Tools.

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## The Third App from J2sw: Prefix Advertisement Checker

DevFeed: [The Third App from J2sw: Prefix Advertisement Checker](<https://devfeed.tech/articles/the-third-app-from-j2sw-prefix-advertisement-checker-40188.md>)

Original publisher: [Read original article](<https://blog.j2sw.com/resources/prefix-advertisement-checker/>)

Author: j2sw

Published: 2026-07-31T12:17:00Z

Content type: tutorial

Language: en

Sources: [Justin Wilson (j2sw)](<https://devfeed.tech/sources/justin-wilson-j2sw.md>)

Topics: [BGP](<https://devfeed.tech/topics/bgp.md>), [networking](<https://devfeed.tech/topics/networking.md>), [App](<https://devfeed.tech/topics/app.md>), [Cisco](<https://devfeed.tech/topics/cisco.md>), [MikroTik](<https://devfeed.tech/topics/mikrotik.md>)

Tags: [application](<https://devfeed.tech/tags/application.md>), [bgp](<https://devfeed.tech/tags/bgp.md>), [irr](<https://devfeed.tech/tags/irr.md>), [j2-networks](<https://devfeed.tech/tags/j2-networks.md>), [j2-updates](<https://devfeed.tech/tags/j2-updates.md>), [network-engineering-resources](<https://devfeed.tech/tags/network-engineering-resources.md>), [network-tools](<https://devfeed.tech/tags/network-tools.md>), [network-troubleshooting](<https://devfeed.tech/tags/network-troubleshooting.md>), [prefix-advertisement](<https://devfeed.tech/tags/prefix-advertisement.md>), [ripe-ris](<https://devfeed.tech/tags/ripe-ris.md>), [roa](<https://devfeed.tech/tags/roa.md>), [routing](<https://devfeed.tech/tags/routing.md>), [routing-policy](<https://devfeed.tech/tags/routing-policy.md>), [rpki](<https://devfeed.tech/tags/rpki.md>), [visibility](<https://devfeed.tech/tags/visibility.md>)

### AI overview

This article describes the J2SW Prefix Advertisement Checker, an application that evaluates an exact IPv4 or IPv6 prefix using live BGP data. It reports observed origin ASNs from RIPE RIS collectors, collector visibility, RPKI/ROA status, and matching IRR route objects, with an optional expected origin ASN for comparison.

### Source excerpt

A prefix can appear in the global BGP table and still have a routing problem. The route may originate from the wrong ASN. Its ROA may also authorize a shorter prefix but reject the advertised prefix length. Checking each part normally means pulling data from several routing tools. The J2SW Prefix Advertisement Checker, my 3rd ... Read more The post The Third App from J2sw: Prefix Advertisement Checker appeared first on Justin Wilson (j2sw).

## Introducing the J2sw MTU and Encapsulation Calculator

DevFeed: [Introducing the J2sw MTU and Encapsulation Calculator](<https://devfeed.tech/articles/introducing-the-j2sw-mtu-and-encapsulation-calculator-40186.md>)

Original publisher: [Read original article](<https://blog.j2sw.com/resources/mtu-encapsulation-calculator/>)

Author: j2sw

Published: 2026-07-28T16:37:53Z

Content type: tutorial

Language: en

Sources: [Justin Wilson (j2sw)](<https://devfeed.tech/sources/justin-wilson-j2sw.md>)

Topics: [Network](<https://devfeed.tech/topics/network.md>), [Tool](<https://devfeed.tech/topics/tool.md>), [Ethernet](<https://devfeed.tech/topics/ethernet.md>), [VXLAN](<https://devfeed.tech/topics/vxlan.md>)

Tags: [calculator](<https://devfeed.tech/tags/calculator.md>), [cisco](<https://devfeed.tech/tags/cisco.md>), [ethernet](<https://devfeed.tech/tags/ethernet.md>), [fragmentation](<https://devfeed.tech/tags/fragmentation.md>), [gre](<https://devfeed.tech/tags/gre.md>), [headers](<https://devfeed.tech/tags/headers.md>), [ipsec](<https://devfeed.tech/tags/ipsec.md>), [ipv4](<https://devfeed.tech/tags/ipv4.md>), [ipv6](<https://devfeed.tech/tags/ipv6.md>), [juniper](<https://devfeed.tech/tags/juniper.md>), [mikrotik](<https://devfeed.tech/tags/mikrotik.md>), [mpls](<https://devfeed.tech/tags/mpls.md>), [mtu](<https://devfeed.tech/tags/mtu.md>), [network-engineering-resources](<https://devfeed.tech/tags/network-engineering-resources.md>), [network-tools](<https://devfeed.tech/tags/network-tools.md>), [network-troubleshooting](<https://devfeed.tech/tags/network-troubleshooting.md>), [overhead](<https://devfeed.tech/tags/overhead.md>), [payload](<https://devfeed.tech/tags/payload.md>), [pppoe](<https://devfeed.tech/tags/pppoe.md>), [vlan](<https://devfeed.tech/tags/vlan.md>), [vxlan](<https://devfeed.tech/tags/vxlan.md>)

### AI overview

The article introduces the J2SW MTU and Encapsulation Calculator, which estimates inner IP MTU and required underlay MTU for combinations of PPPoE, GRE, VLAN, MPLS, VXLAN, and other encapsulations. It explains how Layer 2 tags affect Ethernet frame size separately from IP MTU and describes overhead calculations, including cases where fragmentation can be avoided.

### Source excerpt

Ever wondered what the effects of different combinations of PPPoE, GRE, and others have on the MTU of a packet? I am excited to announce the first of many J2 Network tools: the J2SW MTU and Encapsulation Calculator. You select the service MTU and the encapsulation used on the path. The calculator then works out ... Read more The post Introducing the J2sw MTU and Encapsulation Calculator appeared first on Justin Wilson (j2sw).