Inter-subnet routing in EVPN MPLS Environment

In this article, we will review inter-subnet routing scenarios in EVPN environment. As we will discover, certain topologies might lead to sub-optimal traffic flows within EVPN network.

Our setup will be comprised of three PE and four CE devices as shown below:

Inter-subnet routing in EVPN Environment
Inter-subnet routing in EVPN Environment

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Hot Potato vs Cold Potato Routing

Hot Potato and Cold Potato are two practices of exchanging traffic between BGP Peers. The difference in these two methods is in the approaches to how to carry traffic across the network.

Hot Potato vs Cold Potato discussions are only relevant in the scenarios where multiple traffic exchange (peering) points exist between two networks.

In our example, we will use the following diagrams depicting two networks spanning across North America and Europe.

We are interested in the traffic flow that is originated by Customer-NA connected to ISP-BLUE and is destined to Customer-EU connected to ISP-GREEN.

BGP Hot Potato vs Cold Potato Routing
BGP Network Interconnects

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EVPN Type 5 Configuration Example – Juniper MX


In this example, we will show how to configure L2 and L3 EVPN service on Juniper MX devices.

If you are not familiar with EVPN, please review our introductory articles on EVPN.

In this lab, we will leverage our previous example, where we delivered L2 connectivity between multiple sites, and will augment it with L3 site-to-site connectivity options.

One shared broadcast domain with IP range is used on PE-CE interfaces across the entire network. Each CE site is assigned a unique subnet on LAN interface.

EVPN Type 5 Lab Topology
EVPN Type 5 Lab Topology

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EVPN Type 5 (IP Prefix Route) Explained

EVPN Type 5 route that is proposed in ‘IP Prefix Advertisement in EVPN’ draft is a mechanism to carry IPv4 and IPv6 advertisements in EVPN-only networks. While EVPN Type 2 routes allow to carry both MAC addresses and IP addresses, tight coupling of specific IP addresses with IP Prefixes might not be desirable. Section 2.2 of the draft discusses different scenarios where such coupling is nor desirable.

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EVPN MPLS Service Types Illustrated

EVPN VLAN-Based Service

With this service interface, an EVPN instance consists of only a single broadcast domain (e.g., a single VLAN).  Therefore, there is a one-to-one mapping between a VID on this interface and a MAC-VRF. Since a MAC-VRF corresponds to a single VLAN, it consists of a single bridge table corresponding to that VLAN.

EVPN VLAN-Based Service
EVPN VLAN-Based Service

Click here for Juniper MX Configuration Example.

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EVPN MPLS Service Types

Broadcast Domains


Bridge Table MAC VLAN to MAC-VRF Mapping Ethernet TAG ID VID Translation
VLAN-Based Service Single Single Can overlap between VLANs one-to-one 0 Egress PE
VLAN Bundle Service Multiple Single Unique for all VLANs many-to-one 0 Not Supported
Port-Based Service Multiple Single Unique for all VLAN many-to-one 0 Not Supported
VLAN-Aware Bundle Service Multiple One per VLAN Can overlap between VLANs many-to-one VID or normalized TAG ID


Port-Based VLAN-Aware Service Multiple One per VLAN Can overlap between VLANs many-to-one VID


Not Supported

For more information on EVPN, please refer to our other articles on this topic:

EVPN Type 4 (Ethernet Segment route) Explained

Ethernet Segment Routes are needed in multi-homing scenario and used for Designated Forwarder Election. Designated Forwarder is responsible for sending broadcast, unknown multicast and multicast (BUM) traffic to the CE on a particular Ethernet Segment.

RFC 7432 allows selecting a DF at the granularity of <ES, VLAN> for VLAN-based service and <ES, VLAN bundle> for VLAN-aware service. This enables load-balancing of BUM traffic at a VLAN or VLAN-bundle level.

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EVPN Type 3 (Inclusive Multicast Ethernet Tag route) Explained

Type 3 routes are required for Broadcast, Unknown Unicast and Multicast (BUM) traffic delivery across EVPN networks. Type 3 advertisements provide information about P-tunnels that should be used to send BUM traffic.

Without Type 3 advertisements, ingress router would not know how to deliver BUM traffic to other PE devices that comprise given EVPN instance.

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EVPN Type 2 (MAC/IP Advertisement route) Explained

Type 2 routes are used to advertise MAC addresses and IP addresses that might be associated with aforementioned MAC addresses.

In order to advertise Type 2 routes, PE needs to learn MAC addresses from the directly attached CEs. This is done via normal data-plane learning mechanisms. RFC 7432 also allows for MAC address learning via control plane interaction between PE and CE, although we have not see this implemented by any vendors.

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EVPN Type 1 (Ethernet Auto-Discovery) Explained

Type 1 advertisements are used for two distinct functions – Fast Convergence and Aliasing. EVPN Fast Convergence allows PE devices to change the next-hop adjacencies for all MAC addresses associated with a particular Ethernet Segment. EVPN aliasing allows traffic to be balanced across multiple egress points.

Type 1 routes are only advertised if Ethernet Segment Identifier is set to non-zero value, meaning that Type 1 routes are only originate for multi-homed sites.

Please refer to the following cheatsheet if you are not familiar with EVPN Terminology.

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