Rayhaan JaufeerallyandClaude Fable 5.1
2910a2a800
As presented. The palette is light on request of the reviewer; code blocks and byte dumps keep a dark ground so the byte colours still work. The OPEN walk lights the hovered bytes as an inverted block and its table cells are dark text on a tint of their group colour. build.py inlines reveal.js, the stylesheets, scripts and Markdown sections into slides/dist/hands-on-bgp.html for uploading. Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
106 lines
4.0 KiB
Markdown
106 lines
4.0 KiB
Markdown
# Transit and exchanges
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Notes:
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Section 4. Two very different ways of getting routes, and what an Internet
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exchange physically is.
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---
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## Two ways to reach other networks
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<div class="cols">
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<div>
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### IP transit
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- You **pay** a provider
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- They give you routes to _everyone_
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- They announce you to _everyone_
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</div>
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<div>
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### Peering
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- Usually **free**, by mutual benefit
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- You exchange _your own_ routes, and your customers'
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- Traffic between the locally connected parties only
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</div>
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</div>
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Notes:
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Transit is a customer-provider relationship; peering is between equals. A peer
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does not carry your traffic to third parties. Most networks have both: transit
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as the fallback, peering to keep traffic cheap and close.
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---
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## An exchange is a big Ethernet switch
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<svg class="diagram" viewBox="0 0 1000 400" role="img" aria-label="Members attached to a shared Ethernet peering LAN, with a route server">
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<g class="fabric"><rect x="60" y="175" width="880" height="56" rx="10"/></g>
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<text x="500" y="200" class="accent">peering LAN: one Ethernet segment, one subnet</text>
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<text x="500" y="220" class="small">SwissIX 2001:7f8:24::/64</text>
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<g class="hot"><rect x="70" y="40" width="180" height="70" rx="8"/></g>
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<text x="160" y="70">AS210036</text><text x="160" y="92" class="small">::c9</text>
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<rect x="300" y="40" width="180" height="70" rx="8"/><text x="390" y="70">AS559 SWITCH</text><text x="390" y="92" class="small">::35</text>
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<rect x="530" y="40" width="180" height="70" rx="8"/><text x="620" y="70">AS2906 Netflix</text><text x="620" y="92" class="small">::55</text>
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<rect x="760" y="40" width="180" height="70" rx="8"/><text x="850" y="70">AS13335 Cloudflare</text><text x="850" y="92" class="small">::c0</text>
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<line class="link" x1="160" y1="110" x2="160" y2="175"/><line class="link" x1="390" y1="110" x2="390" y2="175"/>
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<line class="link" x1="620" y1="110" x2="620" y2="175"/><line class="link" x1="850" y1="110" x2="850" y2="175"/>
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<rect x="385" y="300" width="230" height="70" rx="8"/><text x="500" y="330">route servers</text><text x="500" y="352" class="small">AS42476 ::a5ec:a:1</text>
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<line class="link" x1="500" y1="231" x2="500" y2="300"/>
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<path class="bgp" d="M 140 110 C 140 290, 300 335, 385 335"/>
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<path class="bgp" d="M 410 110 C 410 250, 440 270, 470 300"/>
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<path class="traffic" d="M 180 110 C 180 165, 370 165, 370 110"/>
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<text x="275" y="138" class="small" style="fill:#4fd98a">traffic</text>
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<text x="215" y="300" class="small accent">BGP</text>
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</svg>
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Notes:
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Every member plugs one router port into the same layer-2 network and gets one
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address in a shared subnet. No routing inside the exchange: just Ethernet.
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Dashed blue is a BGP session, green is where the packets actually go.
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---
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## What that implies
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- Peering participants in an exchange are all one hop away, found by neighbour discovery
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- A route's next hop is the peer's LAN address, so traffic goes **directly** member to member
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- The exchange is a simple layer 2 switch, allowing for a large capacity at low cost
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- Strict(ish) rules on what traffic is allowed on the peering lan (e.g. no DHCP or broadcast packets)
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Notes:
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- IPv6 neighbour discovery and ARP are used to discover the MAC addresses of peers
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- after which traffic can flow directly
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---
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## Route servers
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Are a piece of shared infrastructure that simplifies peering.
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- Most participants peer with the route server and annouce their prefixes there
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- The route server can then distribute these routes to every other participant
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- Simplifes from `n²` to `n` sessions
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- Not in the traffic path and does not add its own AS into the path
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- Allows controlling behaviour with communities, e.g. `42476:0:<as>` "not to `<as>`", `42476:1:<as>` "only to `<as>`"
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Notes:
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A route server is a BGP speaker that only redistributes. Because it is
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transparent, the AS path looks exactly as if you peered with each member
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directly. We will use those communities in the lab.
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---
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## Looking glasses
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Are a useful tool to inspect the state of another network or internet exchange
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- SwissIX https://lg.swissix.ch/
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- NL-ix https://lg.nl-ix.net/
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- BGP tools https://bgp.tools/
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