Merge pull request #39 from stackhpc/evpn

Add physical network and EVPN fabric documentation

Author: markgoddard

.github/workflows/deployment_yaml/enable-ironic.yml

@@ -5,3 +5,4 @@ ceph_managed: false
 ironic: true
 ironic_automated_cleaning: true
 kayobe_manages_physical_network: true
+physical_network_evpn: true

source/_static/spine-leaf.png

@@ -20,6 +20,9 @@ ironic_automated_cleaning: true
 # Whether Kayobe manages physical network devices.
 kayobe_manages_physical_network: true
 
+# Whether the physical network is an EVPN fabric.
+physical_network_evpn: false
+
 # Whether the deployment includes Wazuh.
 wazuh: true
 

source/data/deployment.yml

@@ -0,0 +1,4 @@
+EVPN VXLAN Fabric details
+=========================
+
+.. Specific details about the client's EVPN fabric should be included here.

source/include/evpn_fabric_details.rst

@@ -0,0 +1,344 @@
+EVPN VXLAN overview
+===================
+
+Ethernet Virtual Private Network (EVPN) is a standard technology that
+can be used for scaling layer 2 networks that is becoming increasingly
+popular. It combines a layer 3 (Equal-Cost Multi-Path)
+ECMP "underlay" fabric with VXLAN "overlays" that stretch VLANs between
+switches.
+
+EVPN is typically used with a spine/leaf network architecture:
+
+.. figure:: _static/spine-leaf.png
+   :alt: Spine/leaf network architecture
+   :class: no-scaled-link
+
+This type of multipath network is resilient to failures of
+individual links or devices. A standard layer 2 (Ethernet) network
+cannot achieve this without introducing forwarding loops or disabling
+links and/or switches (e.g. Spanning Tree Protocol (STP)).
+
+Often the leaf switches will be paired, with MLAG or similar technology
+used to connect servers to both switches in a pair.
+
+Border Gateway Protocol (BGP) is used in the control plane of both the
+underlay and the overlay to exchange connectivity between the switches.
+BGP is a proven, widely used protocol that underpins exchange of routing
+information on the Internet. The underlay uses standard BGP, while the
+overlay uses Multi Protocol BGP (MP-BGP) to exchange MAC addresses and
+other information between Virtual Tunnel Endpoints (VTEPs).
+
+This network architecture is undoubtedly more complex than the standard
+layer 2 networks we have generally used in the past. It's easiest
+to build up the picture in layers.
+
+Underlay IP links
+-----------------
+
+Each leaf switch has a layer 3 (IP) /31 point to point connection to
+each spine switch. Typically we would divide up a supernet (e.g. /24)
+into multiple /31 subnets. Doing this puts the spine-leaf links into
+layer 3 mode.
+
+Example leaf interface config on Dell OS10:
+
+::
+
+   !
+   interface ethernet1/1/1
+    no shutdown
+    no switchport
+    ip address 172.0.0.0/31
+
+Example spine interface config on Dell OS10:
+
+::
+
+   !
+   interface ethernet1/1/1
+    no shutdown
+    no switchport
+    ip address 172.0.0.1/31
+
+One of the implications of this is that each switch and the hosts
+attached to it have become an isolated layer 2 (Ethernet) network.
+
+Another implication is that each switch only has layer 3 (IP)
+connectivity to other neighbouring switches.
+
+On Dell leaf switches with Virtual Link Trunking (VLT, aka MLAG), the
+inter-switch link between leaf switch pairs is also configured with an
+IP point to point link. This ends up getting used more than you might
+expect.
+
+BGP underlay
+------------
+
+In order to stitch together these individual point to point IP fabric
+links, we use a BGP control plane to exchange routing information
+between the switches. This allows each switch to reach (via L3) not only
+its immediate neighbours, but any of their neighbours (and so on). Wait,
+we could build an Internet out of this...
+
+For the BGP underlay, each switch establishes a BGP session with each of
+its immediate neighbours.
+
+Example on Dell OS10 from a Leaf:
+
+::
+
+   # show ip bgp summary 
+   BGP router identifier 172.1.0.0 local AS number 65001
+   Neighbor                                      AS          MsgRcvd     MsgSent     Up/Down           State/Pfx      
+   172.0.0.1                                   65101         22834       22842       1w:6d:18:55:29    34 
+
+The neighbour's IP address (172.0.0.1) is the fabric link partner's IP.
+
+The BGP router identifier (172.1.0.0) is unique to each switch, and
+should be a separate IP range from the fabric links. On Dell OS10
+switches this is assigned to a loopback device as a /32 IP address.
+
+The Autonomous System (AS) number (spine: 65101, leaf: 65001) may be
+assigned to multiple devices. Dell provides various different reference
+configurations which use a single shared AS, or multiple AS. It's not
+clear to me why you would choose one or another approach.
+
+One thing that may not be immediately obvious is that BGP within an AS
+is internal BGP (iBGP), whereas between different AS it is external BGP
+(eBGP).
+
+BGP neighbour info on a Dell OS10 system:
+
+::
+
+   # show ip bgp neighbors 
+   BGP neighbor is 172.0.0.1, remote AS 65101, local AS 65001   external link
+     
+     BGP version 4, remote router ID 172.1.0.1
+     BGP state ESTABLISHED, in this state for 1 weeks 6 days 19:04:49
+     Last read 01:18:01 seconds
+     Hold time is 180, keepalive interval is 60 seconds
+     Configured hold time is 180, keepalive interval is 60 seconds
+     Fall-over disabled
+     
+     Received 22845 messages
+       1 opens, 0 notifications, 15 updates
+       22829 keepalives, 0 route refresh requests
+     Sent 22854 messages
+       1 opens, 0 notifications, 17 updates
+       22836 keepalives, 0 route refresh requests
+     Minimum time between advertisement runs is 30 seconds
+     Minimum time before advertisements start is 0 seconds
+     
+     Capabilities received from neighbor for IPv4 Unicast:
+       MULTIPROTO_EXT(1)
+       ROUTE_REFRESH(2)
+       CISCO_ROUTE_REFRESH(128)
+       4_OCTET_AS(65)
+     Capabilities advertised to neighbor for IPv4 Unicast:
+       MULTIPROTO_EXT(1)
+       ROUTE_REFRESH(2)
+       CISCO_ROUTE_REFRESH(128)
+       4_OCTET_AS(65)
+     Prefixes accepted 34, Prefixes advertised 36
+     Connections established 1; dropped 0
+     Last reset never
+     For address family: IPv4 Unicast
+       Allow local AS number 0 times in AS-PATH attribute
+      Prefixes ignored due to:
+       Martian address  0, Our own AS in AS-PATH 0
+       Invalid Nexthop  0, Invalid AS-PATH length 0
+       Wellknown community 0, Locally originated 0
+     
+     Local host: 172.0.0.0, Local port: 179
+     Foreign host: 172.0.0.1, Foreign port: 44058
+
+We're looking for a BGP state of ESTABLISHED.
+
+Here is a route table on Dell OS10:
+
+::
+
+   # show ip bgp
+   BGP local RIB : Routes to be Added , Replaced , Withdrawn 
+   BGP local router ID is 172.1.0.0
+   Status codes: s suppressed, S stale, d dampened, h history, * valid, > best
+   Path source: I - internal, a - aggregate, c - confed-external,
+   r - redistributed/network, S - stale
+   Origin codes: i - IGP, e - EGP, ? - incomplete
+             Network                                 Next Hop                                Metric         LocPrf         Weight         Path           
+   *         172.0.0.0/31                            172.0.0.1                               0              100            0              65001 ?
+   *         172.0.0.0/31                            172.2.0.5                               0              100            0              65001 ?
+   *>r       172.0.0.0/31                            0.0.0.0                                 0              100            32768           ?
+
+At this point it should be possible to ping the fabric IP address of any
+switch in the network.
+
+On Dell OS this is configured as follows:
+
+::
+
+   router bgp 65001
+    router-id 172.1.0.0
+    !
+    address-family ipv4 unicast
+     redistribute connected
+    !
+    neighbor 172.0.0.1
+     remote-as 65101
+     no shutdown
+     !
+     address-family ipv4 unicast
+      no sender-side-loop-detection
+    !
+
+BGP-EVPN overlay
+~~~~~~~~~~~~~~~~
+
+The MP-BGP overlay is used to share VXLAN connectivity information
+between switches.
+
+On Dell OS10 (from a leaf):
+
+::
+
+   # show ip bgp l2vpn evpn summary 
+   BGP router identifier 172.1.0.0 local AS number 65001
+   Neighbor                                      AS          MsgRcvd     MsgSent     Up/Down           State/Pfx      
+   172.1.0.1                                     65101       29100       33582       1w:6d:19:15:50    295
+
+This may appear similar to the underlay BGP summary, however here the
+neighbours are using the per-switch BGP router ID. This IP is now
+reachable across the IP fabric. Again, each switch establishes a session
+with its immediate neighbours.
+
+BGP neighbour info on a Dell OS10 system:
+
+::
+
+   # show ip bgp l2vpn evpn neighbors 
+   BGP neighbor is 172.1.0.1, remote AS 65101, local AS 65001   external link
+     
+     BGP version 4, remote router ID 172.1.0.1
+     BGP state ESTABLISHED, in this state for 1 weeks 6 days 21:59:35
+     Last read 00:11:56 seconds
+     Hold time is 180, keepalive interval is 60 seconds
+     Configured hold time is 180, keepalive interval is 60 seconds
+     Fall-over disabled
+     EBGP multihop enabled, multihop TTL set to 4
+     
+     Received 39322 messages
+       2 opens, 2 notifications, 21181 updates
+       18137 keepalives, 0 route refresh requests
+     Sent 32041 messages
+       5 opens, 0 notifications, 12303 updates
+       19733 keepalives, 0 route refresh requests
+     Minimum time between advertisement runs is 30 seconds
+     Minimum time before advertisements start is 0 seconds
+     
+     Prefixes accepted 270, Prefixes advertised 163
+     Connections established 2; dropped 2
+     Closed by neighbor sent 1 weeks 6 days 21:59:50 ago
+     Local host: 172.1.0.0, Local port: 41483
+     Foreign host: 172.1.0.1, Foreign port: 179
+
+Again, we're looking for a state of ESTABLISHED. At Habrok we saw the
+BGP session getting to ESTABLISHED, then sometimes flapping after 3
+minutes. This is the default hold time, and would happen when a large
+BGP update occurred, due to an MTU blackhole on the network path (the
+inter-switch link).
+
+So far we have not configured any VXLANs to share information about.
+Let's fix that.
+
+VXLANs
+------
+
+If we return to our mental model of each switch as an isolated layer 2
+Ethernet network, consider connecting up those isolated networks with a
+series of overlay networks, such that a host in VLAN A on switch 1 again
+has direct connectivity to a host in VLAN A on switch 2. We can do this
+using VXLANs. These overlays, or tunnels, are used to encapsulate a
+layer 2 packet within a VXLAN UDP packet. This allows the packet to
+traverse a network with only layer 3 connectivity, such as our underlay
+fabric.
+
+We must create a VXLAN network on each switch that maps to a VLAN.
+
+On a Dell OS10 system, here is one such VXLAN network:
+
+::
+
+   # show virtual-network 10016
+   Codes: DP - MAC-learn Dataplane, CP - MAC-learn Controlplane, UUD - Unknown-Unicast-Drop
+   Virtual Network: 10016
+      Members:
+         VLAN 16: port-channel1000
+      VxLAN Virtual Network Identifier: 10016
+         Source Interface: loopback0(172.2.0.0)
+         Remote-VTEPs (flood-list):
+
+In this case we have VXLAN VNI 10016, which maps to VLAN 16. The source
+interface is loopback0, which we have configured with a /32 IP address
+for the VTEP. In an MLAG scenario , this IP address is shared between
+each leaf switch pair. This IP address is used as the source and
+destination for the outer VXLAN UDP packet.
+
+Currently, there are no remote VTEPs.
+
+EVIs
+----
+
+EVPN Instances (EVIs) are the missing link between the EVPN BGP control
+plane and the VXLAN networks - they define which VXLAN networks will be
+shared via EVPN BGP, and with which switches.
+
+::
+
+   # show evpn evi 10016
+     
+   EVI : 10016, State : up
+     Bridge-Domain       : Virtual-Network 10016, VNI 10016
+     Route-Distinguisher : 1:172.2.0.0:10016
+     Route-Targets       : 0:65001:10016 both, 0:65101:10016 import
+     Inclusive Multicast : 172.2.0.1
+     IRB                 : Disabled
+
+On Dell OS10 switches there is an "auto evi" mode, which automatically
+adds an EVI for each VXLAN. However this doesn't work with the multiple
+AS topology used at Habrok.
+
+The route distinguisher (RD) is an ID for routes shared by this switch.
+The Route Targets (RT) are AS numbers of other switches. Routes can be
+exported, imported, or both. Inclusive multicast defines the list of
+VTEPs to be included in a multicast group for BUM traffic. IRB is
+Integrated Routing and Bridging (IRB), which we'll get onto.
+
+Now that we have an EVI configured for our VXLAN, we now see EVPN
+"routes" for MAC addresses:
+
+::
+
+   *         Route distinguisher: 172.23.62.133:10016 VNI:10016
+   [2]:[0]:[48]:[16:7f:06:fb:02:47]:[0]:[0.0.0.0]/280          172.23.62.133                 0              100            0              65103 65005 ?
+
+The most common type of route is type 2, and this defines MAC address
+routes. Each EVI shares MAC addresses in its local MAC table for the
+VLAN with other EVPN switches, avoiding the "flood and learn" behaviour
+of a static VXLAN configuration. This means that a MAC address lookup on
+switch A will now potentially include remote VTEPs, as well as local
+interfaces.
+
+Integrated Routing and Bridging (IRB)
+-------------------------------------
+
+IRB can be used to perform routing in a distributed manner, across the
+fabric. Typically, each leaf switch is configured as a router, and will
+route on ingress to the destination VXLAN.
+
+Resources
+---------
+
+This explainer series by nullzero is very helpful in building up the
+details in the picture. Here's the first part:
+https://www.nullzero.co.uk/aruba-aos-cx-evpn-vxlan/

source/include/evpn_fabric_overview.rst

@@ -20,6 +20,7 @@ Contents
    introduction
    working_with_openstack
    working_with_kayobe
+   physical_network
    hardware_inventory_management
    ceph_storage
    managing_users_and_projects

source/index.rst

@@ -0,0 +1,19 @@
+.. include:: vars.rst
+
+================
+Physical network
+================
+
+.. ifconfig:: deployment['kayobe_manages_physical_network']
+
+   The |project_name| deployment uses Kayobe to manage the physical network.
+
+   .. ifconfig:: deployment['physical_network_evpn']
+   
+      .. include:: include/evpn_fabric_overview.rst
+   
+      .. include:: include/evpn_fabric_details.rst
+
+.. ifconfig:: not deployment['kayobe_manages_physical_network']
+
+   The |project_name| deployment does not use Kayobe to manage the physical network.