# juniper Published articles for juniper. This is one page of public article previews, not the complete archive. Follow Next page to continue. Summaries are not the original full articles. ## Introducing the J2SW BGP Community Builder DevFeed: [Introducing the J2SW BGP Community Builder]() Original publisher: [Read original article]() Author: j2sw Published: 2026-07-29T18:30:21Z Content type: release Language: en Sources: [Justin Wilson (j2sw)]() Topics: [BGP](), [networking](), [Routing (disambiguation)](), [configuration]() Tags: [aws-direct-connect](), [bgp](), [bgp-communities](), [builder](), [cisco](), [cogent](), [frrouting](), [hurricane-electric](), [juniper](), [mikrotik](), [network-engineering-resources](), [ntt](), [routing-policy]() ### AI overview The J2SW BGP Community Builder helps users select documented provider communities and routing actions, then generates scoped configuration fragments. It includes RFC well-known communities and policies from AWS Direct Connect, NTT DATA, Hurricane Electric, and Cogent Communications, with support for MikroTik RouterOS 7, Cisco IOS-XE, Juniper Junos, and FRRouting. ### Source excerpt The J2SW BGP Community Builder selects documented provider communities and generates scoped policy fragments for MikroTik, Cisco, Junos, and FRRouting. The post Introducing the J2SW BGP Community Builder appeared first on Justin Wilson (j2sw). ## Introducing the J2sw MTU and Encapsulation Calculator DevFeed: [Introducing the J2sw MTU and Encapsulation Calculator]() Original publisher: [Read original article]() Author: j2sw Published: 2026-07-28T16:37:53Z Content type: tutorial Language: en Sources: [Justin Wilson (j2sw)]() Topics: [Network](), [Tool](), [Ethernet](), [VXLAN]() Tags: [calculator](), [cisco](), [ethernet](), [fragmentation](), [gre](), [headers](), [ipsec](), [ipv4](), [ipv6](), [juniper](), [mikrotik](), [mpls](), [mtu](), [network-engineering-resources](), [network-tools](), [network-troubleshooting](), [overhead](), [payload](), [pppoe](), [vlan](), [vxlan]() ### 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). ## -\> BGP handling bug causes widespread internet routing instability DevFeed: [-\> BGP handling bug causes widespread internet routing instability]() Original publisher: [Read original article]() Published: 2025-05-28T13:06:04Z Content type: article Language: en Sources: [BGPexpert](), [benjojo blog]() Topics: [BGP](), [Routing (disambiguation)](), [incident](), [networking](), [Internet Traffic]() Tags: [bgp](), [bug](), [eos](), [incident](), [internet-traffic](), [juniper](), [network](), [route](), [router](), [routing](), [servers]() ### AI overview The article analyzes a May 20, 2025 BGP incident in which a corrupt BGP Prefix-SID attribute containing zeroed internal data interacted with JunOS and Arista EOS behavior. JunOS propagated the message, while Arista EOS devices reset sessions, causing routing instability and potentially brief connectivity loss for some networks. ### Source excerpt benjojo reports: At 7AM (UTC) on Tuesday May 20th 2025 a BGP message was propagated that triggered surprising (to many) behaviours with two major BGP implementations that are often used for carrying internet traffic. This caused a large number of "internet facing" BGP sessions to automatically shut down, causing at the very least some routing instability, and at worst brief loss of connectivity for some networks. BGP implementations failing in various ways after seeing something incorrect/unexpected is definitely not a new thing... ## -\> Enforcing First AS in BGP DevFeed: [-\> Enforcing First AS in BGP]() Original publisher: [Read original article]() Author: lindsay Published: 2023-10-08T14:00:49Z Content type: tutorial Language: en Sources: [BGPexpert]() Topics: [BGP](), [Security](), [Cisco](), [Network](), [Internet]() Tags: [bgp](), [cisco](), [juniper](), [network](), [router](), [security]() ### AI overview This article explains the BGP First AS requirement for eBGP peers, including the security and loop-prevention reasons for enforcing it. It discusses Juniper and Cisco behavior, route-server exceptions at internet exchanges, and the limitation that some routers expose the setting globally rather than per neighbor. ### Source excerpt The BGP RFCs state that external BGP peers should insert their own AS into the AS PATH advertised to eBGP peers. Some peers strip their AS, generally for commercial gain. Juniper and Cisco have opposite default behaviors for handling this. Make sure you set bgp enforce-first-as on Juniper routers. Caveats apply. The annoying part here is that you want to disable this check for internet exchange route servers, but keep it enabled for everything else for security reasons. But that's not universally possible, as on some routers this is a global setting, rather than a per-neighbor one.