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VXLAN > Basics > Flashcards

Basics Flashcards

1
Q

What is the route target notation? And what is the Cisco format for automated derivation?

A

Prefix:Suffix

ASN:VNI

Eg. 65501:50001

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2
Q

How big is a RD / RT in bytes?

A

8 bytes

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3
Q

What is an Overlay?

A

A static or dynamic tunnel that runs on top of a physical network infrastructure

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4
Q

What transport protocol does VXLAN use?

A

UDP

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5
Q

What is frame encapsulation and provide example protocols?

A

Outer tunnel header is L2 MAC, examples are Fabricpath and Trill

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6
Q

Explain MP-BGP

A

Single BGP Peering Session

Carries multiple address families Eg L2VPN EVPN, VPNv4 etc.

Can carry updates for multiple VRFs in one update

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7
Q

Why must MTU be taken into account in VxLAN?

A

MTU must be increased in the Underlay to allow increased packet size due to the fact that the VxLAN header is part of the packet. About 50 bytes extra required.

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8
Q

What is an Underlay in VxLAN?

A

A L3 network used to establish IP reachability between tunnel endpoints. Routing protocol used to advertise these tunnel endpoints.

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9
Q

Name the control plane end host discovery protocol in VxLAN?

A

BGP EVPN

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10
Q

Can multiple VNIs share the same multicast group?

A

Yes, as there are up to 16 million possible VNIs and most hardware only supprts 512 to 1024 multicast groups then this is inevitable.

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11
Q

Name the 5 peices of information that the EVPN address family carries over MP-BGP for VXLAN?

A
  • Host MAC
  • Host IP
  • Network
  • VRF
  • VTEP Information
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12
Q

What is the purpose of EVPN type 3 routes?

A

Create distribution list for ingress replication

New VNI configured, VTEP sends type 3 to each other ingress replication VTEP to inform them of VTEP participating in VNI

Keeps record of who VTEPs need to send BUM traffic to for each VNI

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13
Q

How does VXLAN determine the UDP source port?

A

Hash of the L2/L3/L4 headers from the original frame. Helps with ECMP load-balancing.

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14
Q

Explain the three formats for route distinguishers and what is the default on Cisco devices?

A

Type 0 - 2 byte ASN + 4 byte value

Type 1 - 4 byte IP + 2 byte value

Type 2 - 4 byte ASN + 2 byte value

Default on Cisco switches if auto provisioning is Type 1

RID Loopback IP : internal MAC / VRF ID

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15
Q

What is the purpose of EVPN type 5 routes?

A

transporting IP prefixes

Includes L3 VNI, RT, encap type and next hop VTEP

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16
Q

Explain head end replication and its pros / cons?

A
  • Alternative to multicast
  • every VTEP must be aware of other VTEPS that have membership in a given VNI
  • local VTEP generates n copies of each multidestination packet and it is sent as unicast to each VTEP
  • Con - Additional burden on VTEPs
  • Pro - Reduced complexity in underlay as multicast not required any longer
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17
Q

What is the difference between Unknown Unicast and Broadcast?

A

Unknown Unicast - Endpoint aware of destination MAC but switch isn’t. Potentially switches forwarding table has refreshed and isn’t aware of the MAC any longer, so floods out all interfaces which are part of that VLAN (access and trunk).

Broadcast - Broadcast frame comes from the endpoint with all Fs MAC. Switch sees this and floods out all interfaces which are part of that VLAN (access and trunk).

18
Q

In a leaf / spine architecture, how would you add more port density to the network?

A

Add more leafs

19
Q

What are the mandatory fields within an EVPN type 2 route?

A

MAC Address

MAC Address Length

L2 VNI

20
Q

What is packet encapsulation and provide example protocols?

A

Outer tunnel header is L3 IP, examples and VxLan and LISP

21
Q

What is a hybrid overlay?

A

Mixture of host and network overlays

22
Q

In a leaf / spine architecture, how would you add more bandwidth to the network?

A

Add more spines

23
Q

Describe the two methods used by VxLAN to accommodate overlay BUM traffic in the overlay?

A

Multicast and head end replication

24
Q

Is there still a requirement for flood and learn in BGP EVPN VXLAN?

A

There may be for silent hosts for example, but F&L significantly reduced or even eliminated with BGP EVPN.

25
Q

Explain how VXLAN Flood and Learn works.

A
  • Two end hosts on different VTEPS
  • Both are aprt of same multicast group
  • Same VNI configured on both VTEPS
  • Host A sends ARP
  • VTEP attached to host A receives ARP
  • Encapsulates in VXLAN with source IP of VTEP, destination IP of multicast group, and VNI
  • Sent to core and forwarded to all receivers in multicast group
  • Lands on VTEP, learns MAC to VTEP mapping for source host
  • Decapsulates packet, realises its multidestination and forwards to all interfaces associated with the VNI
  • Host B receives ARP and responds
  • VTEP receives ARP response and does lookup, realises destination is remote VTEP
  • Encapsulates in VXLAn with source VTEP, destination VTEP and VNI and sends
  • VTEP receives and adds mapping for destination IP and VTEP
  • Decaupsulates and forwards to Host A
26
Q

Are route-reflectors used for iBGP or eBGP peering?

A

iBGP

27
Q

What are the three EVPN route types used in Cisco EVPN?

A

Types 2,3,5

28
Q

What are the optional fields within an EVPN type 2 route?

A

IP Address

IP Address Length (/32)

29
Q

What is the purpose of route distinguishers?

A

RDs differentiae between routes stored in the BGP tables

Eg. 192.168.1.0/24 learned from 3 different sites on 3 different VRFs, need a way to distinguish between these routes

Effectively locally significant

30
Q

How is endhost address aging taken care of in VXLAN MP-BGP EVPN?

A

VTEP only sends EVPN update to other VTEPs when an endpoint has aged out. Otherwise, it sends no update and other VTEPs assume that it is still an active endpoint.

31
Q

Name the data plane end host discovery mechanism in VxLAN?

A

Flood and Learn

32
Q

What is the purpose of route targets?

A

Control import and export of prefixes

Routes tagged

Can be identified and placed in different VRF tables

uses import / export keywords under VRFs to import / export routes with particular route targets

33
Q

Describe one major drawback with VXLAN Flood and Learn.

A

Scalability - because flooding still occurs. Becomes a problem in larger networks.

34
Q

What UDP destination port does VXLAN use?

A

4789

35
Q

How does BGP carry host information in a VXLAN network?

A

Using EVPN extensions of BGP protocol.

36
Q

Explain iBGP in a leaf / spine architecture and why route reflectors may be required?

A

Single AS

Information exchange between all speakers in an AS

Route received by one iBGP speaker is not advertised to another iBGP neighbour, therefore, full mesh connectivity required

Utilize route reflectors to remove requirement for full mesh

Spines act as reflectors and reflect routes to any RR clients

Removes requirement for full mesh as leaf switches just need to peer with spines (route reflectors)

Provides greater scalability in control plane

37
Q

What does the diagram demonstrate?

A

VXLAN Flood and Learn

38
Q

What is the difference between a host overlay and a network overlay?

A

Host overlay - software encap / decap on the server (Example ESXi) Network Overlay - hardware encap / decap on the switch (Example Nexus 9K Leaf)

39
Q

What is the purpose of EVPN type 2 routes?

A

MAC / IP address advertisement and reachability

Sent only when host is learned by local VTEP

40
Q

Is MP BGP EVPN an underlay or overlay protocol?

A

Overlay

41
Q

What address is advertised as the next hop in a BGP EVPN advertisment?

A

VTEP

42
Q

What encapsulation number is used in BGP EVPN updates to define VXLAN encapsulation?

A

8

VXLAN (1 decks)

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