Smart Port-Channels

Consider the following output.

How is this possible, when no AAA or Privilege Profiles are configured? Have a look at the interface configuration:

Is this a bug/feature/annoyance. Depending on the platform, this is a feature. This test-interface is part of a port-channel. This is a common operational mistake. How many times has it happened in one of your data centers, where an engineer accidentally made a change to an interface which was a member of a port-channel, only to bring the port-channel and possibly any customer data that traversed the link down?

Continue reading “Smart Port-Channels”

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Cisco OTV (Part III)

This is the final follow-on post from OTV (Part I) and OTV (Part II).

In this final post I will go through the configuration steps, some outputs and FHRP isolation.

OTV Lab Setup

I setup a mini lab using two Nexus 7000 switches, each with the four VDCs, two Nexus 5000 switches and a 3750 catalyst switch.
I emulated two data center sites, each with two core switches for typical layer3 breakout, each with two switches dedicated for OTV and each with one access switch to test connectivity. Site1 includes switches 11-14 (four VDCs on N7K-1) and switch 15 (N5K), whereas Site2 includes switches 21-24 (four VDCs on N7K-2) and switch 32 (3750).

To focus on OTV, I removed the complexity from the transport network by using OTV on dedicated VDCs (four of them for redundancy), connected as inline OTV appliances and by connecting the OTV Join interfaces on a single multi-access network.

This is the topology:

Before configuring OTV, the decision must be made how OTV will be integrated part of the data center design.

Recall the OTV/SVI co-existing limitation. If core switches are in place, which are not the Nexus 7000 switches, OTV may be implemented natively on the new Nexus 7000 switch/es or using a VDCs. If the Nexus 7000 switches are providing the core switch functionality, then separate VDCs are required for OTV.

Continue reading “Cisco OTV (Part III)”

Cisco OTV (Part II)

This is a follow on post from OTV (Part I).

STP Separation

Edge Devices do take part in STP by sending and receiving BPDUs on their internal interface as would any other layer2 switch.

But an OTV Edge Device will not originate or forward BPDUs on the overlay network. OTV thus limits the STP domain to the boundaries of each site. This means a STP problem in the control plane of a given site would not produce any effect on the remote data centers. This is one of the biggest benefits of OTV in comparison to other DCI technologies. This is made possible because MAC reachability information is advertised and learned via the control plane protocol instead of learned using typical MAC flooding behavior.

With the STP separation between sites, the ability for different sites to use different STP technologies is made possible with OTV. I.e., one site can run MSTP while another runs RSTP. In the real world this is a nifty enhancement.

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Multi-Homing

OTV allows multiple Edge Devices to co-exist in the same site for load-sharing purposes. (With NX-OS 5.1 that is limited to 2 OTV Edge Devices per site.)

With multiple OTV Edge Devices per site and no STP across the overlay to shut down redundant links, the possibility of an end-to-end site loops are created. The absence of STP between sites holds valuable benefits, but a loop prevention mechanism is still required, so an alternative method was used. The boys who wrote OTV, decided on electing a master device responsible for traffic forwarding (similar to some non-STP protocols).

With OTV this master elected device is called an AED (Authoritative Edge Device).

An AED is an Edge Device that is responsible for forwarding the extended VLAN frames in and out of a site, from and to the overlay network. It is a very important to understand this before carrying on. Only the AED will forward traffic out of the site onto the overlay. With optimal traffic replication in a transport network, a site’s broadcast and multicast traffic will reach every Edge Device in the remote site. Only the AED in the remote site will forward traffic from the overlay into the remote site. The AED thus ensures that traffic crossing the site-overlay boundary does not get duplicated or create loops when a site is multi-homed.

Continue reading “Cisco OTV (Part II)”

Cisco OTV (Part I)

OTV(Overlay Transport Virtualization) is a technology that provide layer2 extension capabilities between different data centers. In its most simplest form OTV is a new DCI (Data Center Interconnect) technology that routes MAC-based information by encapsulating traffic in normal IP packets for transit.

Cisco has submitted the IETF draft but it is not finalized yet. draft-hasmit-otv-01

OTV Overview

Traditional L2VPN technologies, like EoMPLS and VPLS, rely heavily on tunnels. Rather than creating stateful tunnels, OTV encapsulates layer2 traffic with an IP header and does not create any fixed tunnels.

OTV only requires IP connectivity between remote data center sites, which allows for the transport infrastructures to be layer2 based, layer3 based, or even label switched. IP connectivity as the base requirement along some additional connectivity requirements that will be covered in this post.

OTV requires no changes to existing data centers to work, but it is currently only supported on the Nexus 7000 series switches with M1-Series linecards.

A big enhancement OTV brings to the DCI realm, is its control plane functionality of advertising MAC reachability information instead of relying on the traditional data plane learning of MAC flooding. OTV refers to this concept as MAC routing, aka, MAC-in-IP routinig. The MAC-in-IP routing is done by encapsulating an ethernet frame in an IP packet before forwarded across the transport IP network. The action of encapsulating the traffic between the OTV devices, creates what is called an overlay between the data center sites. Think of an overlay as a logical multipoint bridged network between the sites.

OTV is deployed on devices at the edge of the data center sites, called OTV Edge Devices. These Edge Devices perform typical layer-2 learning and forwarding functions on their site facing interfaces (the Internal Interfaces) and perform IP-based virtualization functions on their core facing interface (the Join Interface) for traffic that is destined via the logical bridge interface between DC sites (the Overlay Interface).

Each Edge Device must have an IP address which is significant in the core/provider network for reachability, but is not required to have any IGP relationship with the core. This allows OTV to be inserted into any type of network in a much simpler fashion.

Lets look at some OTV terminology.

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OTV Terminology

Continue reading “Cisco OTV (Part I)”

Playtime

Its playtime. I am fortunate enough to have the following unboxed and at my disposal for some time.


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It is two Cisco Nexus 7010 chassis, meant for a another new 10Gb DC coming online soon.
Each comprise of the following configuration:

  • 2x SUP-1’s: First generation Supervisor.
  • 3x FAB-1: Cross connect Fabric card module.
  • 2x N7K-M132XP: M1-Series 32-Port 1/10Gb Ethernet Module, 80Gb Fabric.
  • 1x N7K-M148GS: M1-Series 48-Port 1Gb Ethernet Modules, 46Gb Fabric.

The the other switches are:

  • 2x Nexus 5010’s
  • 2x Nexus 2224TP (Fabric Extender)
  • 3x Catalyst 3750G
  • 1x Lost Catalyst 2960.

Unfortunately I do not have a F1 series linecard, it would be interesting testing Cisco FabricPath, but I can test OTV (Overlay Transport Virtualization). The messy cable configuration was done for that exact purpose, to test OTV. ;D

So in the next couple days I will cover the theory, configuration, pro’s and con’s of using OTV as a DCI (Data Center Interconnect).

RBAC with AAA Authentication

A earlier post introduced the Cisco Nexus concept of User Roles, which is a local command authorization method. There are some default system user roles.

RBAC (Role-Based Access Control) is the name/ability to create custom user roles locally on a Cisco Nexus. This gives the administrator the flexibility to define a group of certain commands to be allowed or denied for a selected role. Users can then be designated to belong to certain user roles. This designation can either be done locally on each switch or by using TACACS.

As discussed in the earlier post, AAA authorization and the user roles are mutually exclusive, since AAA Authorization overrides the permissions allowed with user roles. But using RBAC along with AAA Authentication (not Authorization), does bring some neat options to the table, depending obviously on a given network design and requirements.

How does RBAC work?

Custom user roles are defined by giving the role a name and by creating rules within the role. Each rule has a number, to decide the order in which the rules are applied. Rules are applied in descending order. I.e., rule 3 is applied before rule 2, which is applied before rule 1. This means a rule with a higher number overrides a rule with a lower number. Each role may have up to 256 rules configured. All the rules combined within a role determine what operations the role allows the associated user to perform.

Rules can be applied for the following parameters:

  • Command — A command or group of commands defined in a regular expression.
  • Feature — Commands that apply to a function provided by the Cisco Nexus switch.
  • Feature group — Default or user-defined group of features.

Continue reading “RBAC with AAA Authentication”

Cisco Nexus User Roles

IOS relies on privilege levels.  Privilege levels (0-15) defines locally what level of access a user has when logged into an IOS device, i.e. what commands are permitted. This only applies in the absence of AAA being configured. There are 3 default privilege levels on IOS, but really only two that are relevant:

  • Privilege Level 1 — Normal level on Telnet; includes all user-level commands at the router> prompt.
  • Privilege Level 15 — Includes all enable-level commands at the router# prompt.

NX-OS uses a different concept for the same purpose, known as User Roles. User Roles contain rules that define the operations allowed for a particular user assigned to a role. There are default User Roles:

  • Network-Admin—Complete read-and-write access to the entire NX-OS device (only available in the default VDC).
  • Network-Operator—Complete read access to the entire NX-OS device (Default User Role).
  • VDC-Admin—Read-and-write access limited to a VDC (VDCs are not yet available on Nexus 5000).
  • VDC-Operator—Read access limited to a VDC (Default User Role).

A VDC (Virtual Device Context) is a logical separation of control plane hardware resources into virtualized layer3 switches. Don’t worry to much about what a VDC is for now, it is not really relevant to the purpose of this post.

When a NX-OS device is setup for the first time, during the first login, a Network-Admin account must be specified and subsequently be used to login. Arguably a bit more secure that IOS. Any additional users created locally after that will by default receive the User Role “Network-Operator“, unless specified differently:

User Roles are local to a switch and only relevant in the absence of AAA Authorization being configured. To see the permissions of a particular User Role use:

N5K-2# sh role name network-operator
Role: network-operator
  Description: Predefined network operator role has access to all read
  commands on the switch
  -------------------------------------------------------------------
  Rule    Perm    Type        Scope               Entity
  -------------------------------------------------------------------
  1       permit  read

Continue reading “Cisco Nexus User Roles”