Juniper BGP, Configuration Manual

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When the BGP speaker receives an open message from a dynamic peer, the remote
AS number must match one of the following criteria; the connection is closed if it
does not:
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If the peer group has a configured remote AS number, then the received AS
number must be the same as the configured remote AS number.
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If the peer group does not have a configured AS number, then the received AS
number must be consistent with the peer type of the peer group. Use the
neighbor peer-type command to configure the type of the peer-group.
If a peer group has been configured with a peer type but not a remote AS, then the
remote AS for dynamic peers is not known until an open message has been received
from the peer. Until then,
show commands display the remote AS as “ ?” or “
unknown.”
Static peers that you configure with the neighbor remote-as or neighbor peer-group
commands take precedence over the dynamic peers created as a result of the
neighbor allow command. If the remote address of an incoming BGP connection
matches both a static peer and the access list, the static peer is used and no dynamic
peer is created. If you configure a new static peer while a dynamic peer for the same
remote address already exists, BGP automatically removes the dynamic peer.
You can optionally specify the maximum number of dynamic peers that BGP can
create for the peer group. There is no default maximum. In the absence of a specified
maximum, the number of dynamic peers allowed is determined by the available
memory and CPU. Dynamic peers consume about the same resources as static peers.
When the maximum number of dynamic peers has been created for a peer group,
BGP rejects all subsequent connection attempts for that group. This behavior means
that you can specify a maximum to help protect against denial-of-service attacks that
attempt to create many dynamic peers to overwhelm your router resources.
BGP generates a log message whenever a dynamic peer is created, rejected because
the maximum has been reached, or removed. BGP maintains counters for each peer
group for the current number of dynamic peers, the highest number of concurrent
dynamic peers ever reached, and the number of times a dynamic peer was rejected
because the maximum was reached.
Because dynamic peers always fully inherit their configuration from a peer group,
any features that are available for peers but not for peer group members are not
supported for the dynamic peers. Currently, only ORFs are not supported for peer
group members and therefore are not supported for dynamic peers.
clear bgp ipv6 dynamic-peers
clear ip bgp dynamic-peers
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Use to remove all dynamic peers in the specified scope.
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You can specify the IP address of a BGP neighbor or the name of a BGP peer
group as the scope. For IPv4 only, you can also include a VRF in the scope.
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Use the asterisk (*) to remove all BGP dynamic peers.
■
This command takes effect immediately.
48 ■
Configuring BGP Peer Groups
JUNOSe 11.1.x BGP and MPLS Configuration Guide