HON95-wiki/it/network/switching.md

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title: Switching Theory breadcrumbs:

• title: IT
• title: Network --- {% include header.md %}

TODO Organize stuff better. See the config page for STP.

Ethernet Switching Modes

• Store and forward switching:
  • Receive the whole packet befoe forwarding it.
  • Checks integrity.
  • Adds delay.
• Cut-through switching:
  • Start forwarding as soon as the destination address has been inspected.
  • Forwards bad packets.
  • Recuces delay.
• Fragment-free switching:
  • Like cut-through switching, but reads at least 64 bytes before forwarding.
  • Prevent forwarding runt frames, which are less than 64 bytes (the minimum frame length).

Virtual LAN (VLAN)

Q-in-Q

• IEEE 802.1ad/802.1Q.
• For tunneling VLANs using multiple layers of 802.1Q headers.

Virtual Extensible LAN (VXLAN)

• RFC 7348.
• For tunneling VLANs using a UDP overlay network (defauylt port 4789).
• VXLAN network identifiers (VNIs) (24-bit) identify bridge domains.
• VXLAN tunnel endpoints (VTEPs) encapsulate/decapsulate the traffic.
• VTEPs may be either on hosts or on switches/routers as gateways.
• Address learning:
  • Data plane learning: Flood and learn.
  • Data plane learning: Uses BGP to route wrt. MAC addresses.
• BUM handling using multicast:
  • Requires multicast routing-enabled infrastructure.
  • VNI are mapped to multicast groups (N:1).
  • VTEPs joins the groups for its VNIs using IGMP.
  • BUM traffic is only sent to the relevant groups.
• BUM handlign using head end replication:
  • Requires BGP EVPN.
  • Doesn't scale as well as when using multicast.
  • BUM traffic is replicated and sent as unicast to each VTEP that supports the VNI.
• Consider using jumbo frames to avoid fragmentation.

Miscellaneous

• Broadcast, unknown-unicast and multicast traffic (BUM traffic):
  • Generally flooded.
  • Doesn't scale well, which is the primary element of how well L2 domains scale.
  • Throttling and port security helps prevent traffic storms.

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