Konfigurieren Sie Microsoft Windows Server 2016/2019 für die Bereitstellung von DHCP-Diensten für VXLAN (DFA).

To configure DHCP on Windows server. 

1. Create a super scope. Within the super scope, create scope B, S1, S2, S3, …, Sn for the subnet B and the subnets for each segment. 
2. In scope B,  specify the 'Exclusion Range' to be the entire address range (so that the offered address range must not be from this scope). 
3. For every segment scope Si, specify a policy that matches on Agent Circuit ID with value of '0108000600XXXXXX', where '0108000600' is a fixed value for all segments, the 6 numbers "XXXXXX" is the segment ID value in hexadecimal. Also ensure to check the Append wildcard(*) check box. 
4. Set the policy address range to the entire range of the scope.

• Warum wird Microsoft Windows Server 2000/2003/2008 nicht unterstützt?
• Warum ist die Konfiguration in Microsoft Windows Server 2012 so kompliziert?
• Wie einfach ist die Einrichtung in Microsoft Windows Server 2016/2019?

Einführung

Konfiguration des DHCP-Relays in der VXLAN BGP EVPN, DFA-Factory

• Nexus 9000 VXLAN-Konfigurationshandbuch 7.X.
• Nexus 9000 VXLAN-Konfigurationshandbuch 9.3
• DFA (Cisco Dynamic Fabric Automation)

service dhcp
ip dhcp relay
ip dhcp relay information option
ip dhcp relay information option vpn
interface loopback10
  vrf member VRF1
  ip address 10.120.0.1/32 tag 1234567
interface Vlan12
  no shutdown
  vrf member VRF1
  no ip redirects
  ip address 10.120.251.1/24 tag 1234567
  no ipv6 redirects
  fabric forwarding mode anycast-gateway
  ip dhcp relay address 10.0.0.5
  ip dhcp relay source-interface loopback10

RFCs, die im Betrieb des DHCP-Relay-Dienstes in VXLAN BGP EVPN-Fabriken implementiert sind

• RFC, Nexus 9000 v9.3
• RFC, Nexus 9000 v7.x

•	Sub-option 151(0x97) - Virtual Subnet Selection (Defined in RFC#6607)
Used to convey VRF related information to the DHCP server in an MPLS-VPN and VXLAN EVPN multi-tenant environment.

•	Sub-option 11(0xb) - Server ID Override (Defined in RFC#5107.) 
The server identifier (server ID) override sub-option allows the DHCP relay agent to specify a new value for the server ID option, which is inserted by the DHCP server in the reply packet. This sub-option allows the DHCP relay agent to act as the actual DHCP server such that the renew requests will come to the relay agent rather than the DHCP server directly. The server ID override sub-option contains the incoming interface IP address, which is the IP address on the relay agent that is accessible from the client. Using this information, the DHCP client sends all renew and release request packets to the relay agent. The relay agent adds all of the appropriate sub-options and then forwards the renew and release request packets to the original DHCP server. For this function, Cisco’s proprietary implementation is sub-option 152(0x98). You can use the ip dhcp relay sub-option type cisco command to manage the function.

Sub-option 5(0x5) - Link Selection (Defined in RFC#3527.) 

The link selection sub-option provides a mechanism to separate the subnet/link on which the DHCP client resides from the gateway address (giaddr), which can be used to communicate with the relay agent by the DHCP server. The relay agent will set the sub-option to the correct subscriber subnet and the DHCP server will use that value to assign an IP address rather than the giaddr value. The relay agent will set the giaddr to its own IP address so that DHCP messages are able to be forwarded over the network. For this function, Cisco’s proprietary implementation is sub-option 150(0x96). You can use the ip dhcp relay sub-option type ciscocommand to manage the function.

Cisco DHCP Microsoft Windows Server 2012

If multiple DHCP Scopes are required for multiple subnets, you need to create one LoopbackX per subnet/vlan on all LEAFS and create a superscope with a loopbackX range scope and actual client IP subnet scope per vlan.

Create Superscope for all scopes you want to use for Option 82-based policies.
Note
The Superscope should combine all scopes and act as the administrative boundary.

Let us assume the switch is using the address from subnet B (it can be the backbone subnet, management subnet, or any customer designated subnet for this purpose) to communicate with the Windows DHCP server. In DFA we have subnets S1, S2, S3, …, Sn for segment s1, s2, s3, …, sn. 

To configure DHCP on Windows server. 

1. Create a super scope. Within the super scope, create scope B, S1, S2, S3, …, Sn for the subnet B and the subnets for each segment. 
2. In scope B,  specify the 'Exclusion Range' to be the entire address range (so that the offered address range must not be from this scope). 
3. For every segment scope Si, specify a policy that matches on Agent Circuit ID with value of '0108000600XXXXXX', where '0108000600' is a fixed value for all segments, the 6 numbers "XXXXXX" is the segment ID value in hexadecimal. Also ensure to check the Append wildcard(*) check box. 
4. Set the policy address range to the entire range of the scope.

DHCP unter Microsoft Windows Server (Superscope & Policy)

Superscope

Superscope is an administrative feature of a DHCP server that can be used to group multiple scopes as a single administrative entity. Superscope allows a DHCP server to provide leases from more than one scope to clients on a single physical network. Scopes added to a superscope are called member scopes.

Politik

The DHCP Server role in Windows Server 2012 introduces a new feature that allows you to create IPv4 policies that specify custom IP address and option assignments for DHCP clients based on a set of conditions.

The policy based assignment (PBA) feature allows you to group DHCP clients by specific attributes based on fields contained in the DHCP client request packet. PBA enables targeted administration and greater control of the configuration parameters delivered to network devices with DHCP.

Hauptteil

Warum wird Microsoft Windows Server 2000/2003/2008 nicht unterstützt?

1. Eine Anfrage vom Client wird an Broadcast (DHCP Discover) gesendet.
2. Geräte (Nexus) senden ein Paket an einen DHCP-Server (DHCP Discover + Option 82).
3. Der DHCP-Server akzeptiert das Paket, verarbeitet es, sendet es zurück, jedoch ohne Option 82. (DHCP-Angebot - ohne Option 82)
4. Geräte (Nexus) empfangen ein Paket von einem DHCP-Server. (DHCP-Angebot) Sendet dieses Paket jedoch nicht an den Endbenutzer.

Sniffer-Daten - unter Windows Server 2008 und auf dem DHCP-Client

Windows Server 2008 . (Option 82 )

Windows Server 2008 . (Option 82 )

– DHCP Discover DHCP Offer

:

NEXUS-9000V-SW-1# show ip dhcp relay statistics 
----------------------------------------------------------------------
Message Type             Rx              Tx           Drops  
----------------------------------------------------------------------
Discover                  8               8               0
Offer                     8               8               0
Request(*)                0               0               0
Ack                       0               0               0
Release(*)                0               0               0
Decline                   0               0               0
Inform(*)                 0               0               0
Nack                      0               0               0
----------------------------------------------------------------------
Total                    16              16               0
----------------------------------------------------------------------

DHCP L3 FWD:
Total Packets Received                           :         0
Total Packets Forwarded                          :         0
Total Packets Dropped                            :         0
Non DHCP:
Total Packets Received                           :         0
Total Packets Forwarded                          :         0
Total Packets Dropped                            :         0
DROP:
DHCP Relay not enabled                           :         0
Invalid DHCP message type                        :         0
Interface error                                  :         0
Tx failure towards server                        :         0
Tx failure towards client                        :         0
Unknown output interface                         :         0
Unknown vrf or interface for server              :         0
Max hops exceeded                                :         0
Option 82 validation failed                      :         0
Packet Malformed                                 :         0
Relay Trusted port not configured                :         0
DHCP Request dropped on MCT                      :         0
*  -  These counters will show correct value when switch 
receives DHCP request packet with destination ip as broadcast
address. If request is unicast it will be HW switched
NEXUS-9000V-SW-1#

Warum ist die Konfiguration in Microsoft Windows Server 2012 so kompliziert?

• Microsoft Windows Server 2012 verfügt über einen Superpool (SuperScope), in dem Loopback-Adressen und -Pools für echte Netzwerke vorhanden sind.
• Die Wahl des Pools für die Ausgabe der IP-Adresse fällt in SuperScope, da die Antwort vom DHCP-Relay von der in SuperScope enthaltenen Quell-Loopback-Adresse kam.
• Mithilfe einer Richtlinienanforderung wird aus Superscope der Mitgliedsbereich ausgewählt, dessen VNI in Option 82 Suboption 1 Agent Circuit ID enthalten ist. ("0108000600" + 24 VNI-Bits + 24 Bits, deren Werte ich nicht kenne, aber der Sniffer zeigt die Werte 0 in diesem Feld an.)

Wie einfach ist die Einrichtung in Microsoft Windows Server 2016/2019?

• Können wir auf Superscope verzichten?
• Können wir auf Richtlinien verzichten und VNI in eine hexadezimale Form übersetzen?
• Können wir auf Scope for Loopback-DHCP-Quelladressen verzichten?

 Note
All relay agent IP addresses (GIADDR) must be part of an active DHCP scope IP address range. Any GIADDR outside of the DHCP scope IP address ranges is considered a rogue relay and Windows DHCP Server will not acknowledge DHCP client requests from those relay agents.

A special scope can be created to "authorize" relay agents. Create a scope with the GIADDR (or multiple if the GIADDR's are sequential IP addresses), exclude the GIADDR address(es) from distribution, and then activate the scope. This will authorize the relay agents while preventing the GIADDR addresses from being assigned.

• Erstellen Sie einen Pool für Quellrelaisadressen.
• Erstellen Sie einen Pool für Client-Netzwerke

• Richtlinie erstellen
• Erstellen Sie SuperScope

Beispiel

DHCP ( 2 DHCP — VXLAN )

:

( — ):

Source DHCP Relay ( ):

Konfigurieren Sie den DHCP-Dienst unter Microsoft Windows Server 2019

Loopback (source) DHCP Relay.

(Scope) IPv4.

. «Next >»

(Description) .

IP Loopback .

. .

. «Next >»

: DHCP (DNS, WINS, Gateway, Domain) . , . .

, , . «Finish»

. — Scope — «Activate».

/.

.

. «Next >»

(Description) .

IP Loopback .

. ( ) «Next >»

. «Next >»

: DHCP (DNS, WINS, Gateway, Domain) . .

.

DNS .

IP WINS .

Scope.

. «Finish»

Fazit

Liste der Quellen

1. Nexus 9000 VXLAN-Konfigurationshandbuch 7.x.
2. Nexus 9000 VXLAN-Konfigurationshandbuch 9.3
3. DFA (Cisco Dynamic Fabric Automation)
4. Konfigurieren von Microsoft Windows Server 2012 für die Bereitstellung von DHCP-Diensten in einem eVPN-Szenario (VXLAN, Cisco One Fabric usw.)
5. 3.4 DHCP-Superskope
6. Einführung in DHCP-Richtlinien
7. Win2k8 R2 DHCP-Problem mit Option82
8. Auswahloptionen für DHCP-Subnetze